BA038 (B777) Thread

[gas path]

It seems odd that nothing has arisen in the more than 9 months since the accident (and especially since the Northern Hemisphere Winter is near enough here) to actually guide airlines in possible ways to minimise a re-occurance of such an incident.

There are new procedures in place for flight crew during flight and engineering prior to flight, to ensure fuel moves!

[FlyGooseFly!]

Smilin_Ed posted:-
I've read all the previous 2012 posts. Unless I missed something, it has been conclusively shown that the fuel metering valves moved to the full open position but there was no fuel to move through them. Since the valves opened, how could it be a software problem? The system responded to the movement of the throttles. The engines failed because of a scarcity of burnable materials to pass through that system

I have also read all posts on this and other disasters - though I must enter pleading at being most confused at times by disjointed thread creep - I think I've stayed on track and the one overiding factor common to all is that despite many "experts" on aircraft systems and engineering there seems to be a plethora of "conclusively proved" items that turn out to be absolutely wrong and "impossibilities" that turn out to be anything but.

I am reminded of the expert poster with years of experience in oxygen bottles saying that one had never let go in an aircraft and people suggesting they should be sectioned - yet a large part of one had come through the floor to embed itself in the doorframe - visible to all who looked. We also had explosive experts saying that the viewable photos were not of an explosion and other guys confidently pronouncing metal fatigue - all wrong.

In this particular case it certainly seems that the fuel pumps were fighting against something but ice to me is just a convenient answer when nothing else seems to fit. Just how easy is it for some valves to be closed against the pumps? Does anyone know ? Of course, if the actual temperature of the fuel was known we wouldn't be arguing.

[lomapaseo]

FlyGooseFly

I think I've stayed on track and the one overiding factor common to all is that despite many "experts" on aircraft systems and engineering there seems to be a plethora of "conclusively proved" items that turn out to be absolutely wrong and "impossibilities" that turn out to be anything but.


In threads like this you have to read much deeper than individual posts. While I'll admit that the obvious hunches do vary and are discarded along the way as available evidence surfaces, only as ignorance would one profess a conclusively proven point before the final report of facts and analysis is presented. In almost al cases, portions of the postulations of causes have arguments of pro and cons in their consideration, and it is those arguments that become the basis for the support of readership of these threads.

I suggest that you do not assign words like "conclusively proven", "absolutely wrong" or "impossibility" to postulations within these type of discussion threads.

[Rightbase]

Of course, if the actual temperature of the fuel was known we wouldn't be arguing.

Photographic evidence posted earlier shows the fuel was cold enough to cause frost on the lower wing surface.

[Basil]

Rightbase,
Photographic evidence posted earlier shows the fuel was cold enough to cause frost on the lower wing surface.
That's an everyday occurrence following high alt coldsoak as is also frost on upper surface.

[exeng]

Frost on the lower wing surface.

In 30 years or more it is only on very short sectors (i.e. less than 3 hours) that I haven't experienced that. With TAT's on the nippy side of comfortable what can anybody expect?


Regards
Exeng

[TyroPicard]

Perhaps an engineer could confirm this....
There is a difference between the Trent and the GE90 in terms of fuel piping layout. If I interpret correctly the various photos I have googled the GE engine has all the fuel pipery and pumps around the core. On the Trent the fuel starts outside the fan casing and then goes through pipes which pass through the fan airflow on their way to the core.
True or false?

[sooty655]

There is a difference between the Trent and the GE90 in terms of fuel piping layout. If I interpret correctly the various photos I have googled the GE engine has all the fuel pipery and pumps around the core. On the Trent the fuel starts outside the fan casing and then goes through pipes which pass through the fan airflow on their way to the core.



The Trent certainly has some fuel system components mounted on the outside of the fan case. I'm not certain but afaik the GE90 has all the system mounted on the core.

However, both engines have to get the fuel through the fan airflow. The only difference is which components are outside and which are inside.

[Smilin_Ed]

I had envisioned the fuel heater in the wing. From reading this, I gather that it is in the engine nacelle. It looks to me like they needed one in the wing before the pipes enter the engine pylon.

[Green-dot]

I had envisioned the fuel heater in the wing.


There are hydraulic oil-to-fuel heat exchangers.
- 1 heat exchanger in the left main tank for the left hydraulic system,
- 2 heat exchangers in the right main tank for the center and right hydraulic systems.

Through the heat exchangers fuel cools the hydraulic oil but due to the large volume of fuel, heating of the fuel is negligeble.

Regards,
Green-dot

[sooty655]

Green-dot :-
Through the heat exchangers fuel cools the hydraulic oil but due to the large volume of fuel, heating of the fuel is negligeble.



Same applies to the Fuel Oil Heat Exchanger (also known as a fuel-cooled oil cooler). It is controlled only on oil temperature. Any heating of the fuel is co-incidental and uncontrolled.

[john clements]

sorry, gentlemen and ladies,

there's abit about fuel management...centre tank runs to x -thousand
lbs./kgs and then stays off until main tanks reduce to y-thousand, then
centre tank pumps run again. could this have been shortly before the approach commenced ? possibly bringing very cold fuel into the situation?

been following thread for some time....

well done all crew, especially the f/o!

[Green-dot]

there's abit about fuel management...centre tank runs to x -thousand
lbs./kgs and then stays off until main tanks reduce to y-thousand, then
centre tank pumps run again.


Not quite, to be more precise the centre tank override jettison (OJ) pumps are switched off manually at approx. 800kg of fuel remaining in the centre tank. Float-operated shutoff valves prevent fuel scavenge when the main tanks are full. When the main tanks reduce to y-thousand the float-operated shutoff valves open and the fuel scavenge jet pumps will start scavenging (operated by motive flow from the boost pumps) the remaining fuel from the centre tank. The centre tank OJ pumps remain switched off.

Centre tank fuel is relatively warmer than main tank fuel because most of the centre tank is situated above the airconditioning system which radiates heat, it is between forward and aft cargo compartments, and the passenger cabin is above it. Hence, main tank fuel is relatively colder than centre tank fuel.


Green-dot

[MOLWillie]

Was any impact damage to the impeller blades found in the wing tank(s) pump(s) ?

[GFYA]

To answer one of Sooty655's previous postings:

You are correct in the understanding that Rolls-Royce RB211 and it's Trent derivatives have the Fuel Control System mounted on the outside of the Fan case where General Electric have generally favoured mounting much of it's systems around the core.

There are pros and cons for both design philosophies. Whilst at first glance it seems a good plan to keep all the fuel system nice and warm by keeping it close to the core, the transient extremes of temperature encountered during flight in such circumstances impose design issues regarding valve tolerances/clearances. There can also be problems with fuel laquering of metering and control valves that operate in fuel luricated systems caused by higher fuel temperatures.

To answer your question though, the RB211-Trent 895 (and all it's RB211 predecessors way back to the original -22B variant of the late 60s/70s) have the following mounted on the fan case:

Low Pressure Fuel Pump
Low Pressure Fuel filter
Fuel Oil Heat Exchanger
High Pressure Fuel Pump
Fuel Metering Unit (and it's constituent control system)
Fuel Manifold Drains Tank and it's ejector pump.


As an aside, the Main Engine Fuel pump designed and fitted to the R-R Trent 895 may well have demonstrated evidence of bearing face cavitation upon strip, however on such pump designs there is no escaping cavitation and it is more a case of designing the pump to minimise what cavitation there is and to encourage the cavitation to take place in the least problematic areas of the unit - more akin to 'managing' the cavitation than anything else . It is the degree and agressiveness of the cavitation scarring that tell the story of the unit's unhappy existence up to it's untimely death and from what information I have seen, the unit was in good health up until a short time before the incident.

The manufacturer of the pump are very well respected in the Industry and were selected by Rolls-Royce for designing a product with a good pedigree and having an extremely good record for dealing with cavitation issues. The pump itself has a delivery capacity that far exceeds the requirements of the 95,000 lb thrust variant fitted to the R-R powered BA 777 as it was targeted for a much higher thrust Trent variant that didn't make it into production for reasons other than design viability or reliability. Having been closely involved in the project's design, I can say with a high degree of confidence that even in the pump's post cavitation degraded state I can not imagine a situation where the pump was incapable of delivering the required fuel other than through starvation/blockage.

I realise that I have probably re-iterated some points previously made and for that I apologise.

GFYA

[Chris Scott]

Thanks, GFYA,

How clear and illuminating. 2035 (+) posts on this thread, and many on its predecessor, since 17th January. How forbearing of you not to comment until now.

Guess you must have been occupied elsewhere... Welcome back.

Any comment on the theoretical relative susceptibility (to icing blockage) of large cross-section plumbing - versus smaller?

[lomapaseo]

GFYA

I have seen, the unit was in good health up until a short time before the incident.


I may have been reading more into this than intended but should I interpret that the unit did suffer some ill health shortly before the accident?

[ChristiaanJ]

Guys,
Be reasonable, and read GFYA's post properly.
He is saying cavitation damage may be pointing a finger, but is not unique to this case, if I read it properly.

lomapaseo, I agree he should explain what he means with "I have seen, the unit was in good health up until a short time before the incident."

Chris Scott, We're not all frequent PPRuNe readers.....
It's true nobody really answered your post about "large cross-section plumbing" either....which I thought made sense.

CJ

[phil gollin]

Thank-you GFYA, very informative.

I would highlight SOME of your post, for others who have posted since - although it should be read as a whole :

".............. the Main Engine Fuel pump ........... may well have demonstrated evidence of bearing face cavitation upon strip, however on such pump designs there is no escaping cavitation .......... and from what information I have seen, the unit was in good health up until a short time before the incident.

............ The pump itself has a delivery capacity that far exceeds the requirements of the 95,000 lb thrust variant fitted ............. I can say with a high degree of confidence that even in the pump's post cavitation degraded state I can not imagine a situation where the pump was incapable of delivering the required fuel other than through starvation/blockage."


Very Thought provoking.

.

[Flaperon777]

Hey.My first post here so please go easy.
Just wondering,any particular (minimum) amount fuel quantity in the centre tanks before you manually switch them off? Or is it procedure to just put the pumps off when the "fuel low centre" message pops up?
Thx in advance.

[L337]

7 posts before you by Green Dot:

the centre tank override jettison (OJ) pumps are switched off manually at approx. 800kg of fuel remaining in the centre tank. Float-operated shutoff valves prevent fuel scavenge when the main tanks are full. When the main tanks reduce to y-thousand the float-operated shutoff valves open and the fuel scavenge jet pumps will start scavenging (operated by motive flow from the boost pumps) the remaining fuel from the centre tank. The centre tank OJ pumps remain switched off.

[Flaperon777]

Thx.
I just hadnt understood the term "OJ".
Now i think i understand........
I assume these are the same as the centre tank fuel boost pumps.

[Green-dot]

Flaperon777,

I assume these are the same as the centre tank fuel boost pumps.


Yes, basically they are centre tank boost pumps but they have a dual function and therefore are officially named Override / Jettison pumps because they:
a. deliver a higher boost pressure than the main tank boost pumps to ensure the centre tank empties before the main tanks (they override the main tank boost pumps which normally also operate while fuel is fed to the engines from the centre tank).
b. they also function as jettison pumps in case a situation develops whereby fuel needs to be dumped.


Green-dot

[Flight_Idle]

Can anyone provide a photograph of the fuel cooled oil cooler pipe matrix? because I am having difficulty visualizing the following scenario:

Aircraft takes off with 5 litres of water in tanks (AAIB) IF none passes through engines in normal manner & IF it evenly distributes itself evenly between engines, it means that a maximum of 2.5 litres of frozen water managed to block both oil coolers within seconds of each other (with a bit of uneven distribution, less than 2.5 litres would have caused blockage).

If as has been stated in a previous post, the primary purpose is to cool oil & any fuel heating is a secondary uncontrolled effect, one would have thought that a some sort of fuel bypass woud have been designed in to counter any possibility of ice blockage.

I have no experience of modern airliners but I have 35 years experience on the engineering side of older military aircraft. I am desperately trying to visualize how such a small quantity of water could cause such problems, in fact to tell the truth, I don't believe it.

Regards Flight_Idle

[GFYA]

- Chris Scott.

As you can see, I am not a frequent poster on Pprune, more of a watcher. The quiet one on the night out if you will, the one that listens to what others have to say and only infrequently comments with a few 'golden nuggets'. Part of that is a result of how busy this year has been for me and the rest is how frequently I see things get taken out of context on internet forums. That is no reflection on you guys who have remarked since my posting, merely my general perception of such facilities.

WRT your remark regarding icing and pipe diameter, there will of course be a far greater susceptibilty for blockage of narrow Internal diameter fuel pipework. I don't have any facts or figures to present to you I'm afraid, but fuel system icing is taken very seriously in gas turbine design and many components are tested on rigs using fuel that does not have the FSII (Fuel System Icing Inhibitor) additive included.

Having come into this discussion somewhat late, I hope you'll forgive me for not reading all the previous (2035 was it?) postings so I will apologise once more if I touch on issues that have already been addressed.

The RB211-Trent LP fuel filter has a dual purpose, not only will it filter out rubbish/swarf etc that may remain in the fuel tanks after the manufacture of the aircraft or post maintenance, it also filters out ice crystals. Any blockage of the LP fuel filter beyond a critical pressure differential will give rise to the LP fuel filter bypass valve opening and an associated caution and chime in the flightdeck. I am not aware of any such bypass taking place and would have thought that the AAIB report would have declared a filter bypass in their reports.

It is also indicated that there was at least a certain amount of fuel flowing through the pump and metering system because:

a) The engines did not flame out and;

b) The Fuel Metering Valve position is controlled using the fuel pressure delivered by it's associated high pressure fuel pump. By that you may interpret that if there is no fuel flow or pressure that Metering Valve cannot move. In this accident the Fuel Metering Valve operated exactly as per the requirements of the FADEC closed loop software.

In crude terms, the FADEC has a spreadsheet, if you will, of typical Power Lever Angle vs Fuel Metering Valve position vs Engine power output. In this case the Engine power output was significantly less than that expected for the Power Lever Angle. In response to this the FADEC scheduled the Fuel Metering Valve to open further in response to this shortfall. The engines did not respond accordingly.


- Lompaseo.

My comment regarding evidence of ill health before the accident is a result of remarks made in the AAIB report that an unexpected degree of cavitation was found post unit strip at the pump manufacturer's facility. I was not suggesting that there were indications that the pump was about to fail. Far from it, it was a very good pump design. My interpretation of the AAIB's remarks wrt the cavitation found in the subject pumps is that the cavitation scarring is indicative of the pump working in pressure and flow conditions that it was not dsigned for. In this situation, a very low pump outlet pressure.


- Christiaan J:

Thank you for you remarks, may be I should speak up more often?

Absolutely right Sir, my comments about pump cavitation were not suggesting that the degree of cavitation was the cause of the failure, more the symptom.

Regards,

GFYA.

[sky9]

GFYA
Could the cavitation damage be due to the blockage in the fuel lines restricting the amount of fuel to less than demanded, effectively causing the fuel pumps to stall and further reduce fuel flow to the engine? The engines did initially accelerate then fall back.

[GFYA]

Sky9,

Yes, blockages do indeed aggravate cavitation in such pump designs, personally I wouldn't have used the term 'stall' though. I must re-iterate the point that cavitation in such gear pump designs is a given. The important factor is the severity of the cavitation scarring. This is influenced by the specifics of the pump design and the environment in which it is operating. Given the wealth of experience the pump manufacturer had, the design was well understood and was a development of a previous model with a very significant back catalogue of service history. It is the environment (ie the local fuel pressure in the pump) that I feel influenced the degree of cavitation scarring.

Regards,

GFYA

[Machaca]

The fuel cooled oil cooler (FCOC)

http://i337.photobucket.com/albums/n385/motidog/FCOC-cutaway.jpg

is mounted near the top on the fan case right side (black in photo)

http://i337.photobucket.com/albums/n385/motidog/800-79b.jpg

and connected to the gear driven pumps at bottom of engine via a network of tubes:

http://i337.photobucket.com/albums/n385/motidog/800-66b.jpg

[Flight_Idle]

Thanks for those photos Machaca, I assume that the oil passes through the capillary pipes & the fuel passes over them?.

I wonder if the oil is pumped through on a constant flow basis, or is there a mechanism for the oil to be pumped through intermittently to keep engine oil temperature within specified limits?

If the latter stationary oil in the FCOC would reach fuel temperature, would oil viscosity be OK at this temperature?, if this was the case no fuel heating would occur.

Thanks again for the excellent photos.

[sooty655]

Flight_Idle
I assume that the oil passes through the capillary pipes & the fuel passes over them?.



Afaik it's the other way round. The fuel makes a single uncontrolled pass through the tubes. The oil passes around the outside of the tubes, guided by the baffles.

Oil temperature is controlled by a thermostatic valve, which allows the oil to bypass the cooler unless cooling is required.

[Whippersnapper]

Didn't the AAIB initial enquiry state that the pump cavitation was consistent with an aircraft of its age and was unrelated? And why would the fuel freeze during the approach, 30 minutes or more after starting descent and the fuel beginning to warm up again? Surely fuel temperatures are at their lowest at the beginning of the descent, not the bottom of it?

[TheShadow]

Whippersnapper says: "....why would the fuel freeze during the approach, 30 minutes or more after starting descent and the fuel beginning to warm up again? Surely fuel temperatures are at their lowest at the beginning of the descent, not the bottom of it?"

Pretty simple stuff.
Any mass of ice forming in the high-level cruise and adhering to a surface would, in a gradually warming environment of a descent, firstly become dislodged,move with the flow and then lodge somewhere downstream in the fuel-flow and cause an obstruction to that flow.

That simple deduction is a direct pointer to the true nature of BA038's problem.

[exeng]

I don't really see how you could make that 'simple deduction'. How can you come to that conclusion?

Whilst I think I know something about the characteristics of cold fuel and ice formation I have seen nothing from the AAIB releases that specifically points you to your deduction.

It is very difficult to prove anything about this incident because it would seem the evidence melted!


Regards
Exeng

[PETTIFOGGER]

Whippersnapper,
The AAIB's theory is that ice had (probably) adhered to the walls of the fuel feed pipes in the wings and was released during the descent (because of the increase in temperature) causing a restriction in fuel flow at the FOHE. They have been unable to simulate the operational environmental conditions to cause a rollback, except by shoveling lots of ice into their test rig just before the FOHE. There is doubt that the amount of water believed to be in the tanks of G-YMMM could produce the amount of ice required to restrict the fuel flow in this manner. This is a simple precis of part of the AAIB's findings so far, and is an inadequate substitute for their report. Their investigations continue.

[phil gollin]

Pettifogger,

I think calling the AAIB suggestion a "theory" is a little bit too optimistic - they do not think there was enough water to form sufficient ice, and can't model a reasonable event to cause damage.

I think it is merely something they are investigating.


.

[lomapaseo]

Phil Golin


I think calling the AAIB suggestion a "theory" is a little bit too optimistic - they do not think there was enough water to form sufficient ice, and can't model a reasonable event to cause damage.

I think it is merely something they are investigating

good explanation.

It would be nice if we on Pprune could agree on the use of words like "theory", "postulation" and "speculation"

If a consensus can agree I'm willing to adopt them

my current use is:

"theory" starts with a premise at the beginning while explaining links in the chain and ends with a conclusion to the exclusion of all other paths (linkages)

"postulation" starts with a premise anywhere in the chain of events and only to explain the linkage to another link in the chain

"speculation" starts with a premise and jumps directly to a conclusion while excluding confirmation of the links in the chain

My current creed is:

I am inclined to start with "postulations" and only after I see enough links fitting that postulation do I assign a "theory" to it.

I take "cons" against a theory as serious as I do the "pros"

I apply Occams razor to determining both the "Pros" and the "cons"

[Green-dot]

Or perhaps "hypothesis", an unproved theory, tentatively accepted to explain certain facts or to provide a basis for further investigation.


Green-dot

[lomapaseo]

Or perhaps "hypothesis", an unproved theory, tentatively accepted to explain certain facts or to provide a basis for further investigation.


Green-dot

fine by me, is this a substitue for postulation or an "as-in"

Incidently I'm fine with folks who openly hypothesize and/or postulate and/or even theorize later after many facts are known but not with speculation as it wastes time and gives the appearance to the casual reader that one can conclude

[ChristiaanJ]

Green-dot, lomapaseo,
Funny, really.
I've always used "working hypothesis" as my 'worldview system'.

As a mere human, with limited knowledge, that's all one can do.

To me, "God" is a convenient hypothesis thought up by primitive people thousands of years ago to explain phenomena unexplainable to them at that time (be it thunder, or chance).

We no longer need "God" for that.

But we all need a "working hypothesis" about the world around us. Sadly, too many people revert to "belief", instead.....

CJ

[CONF iture]

What is a typical fuel flow at flight idle in landing configuration with engine anti-ice selected on ?
Is it correct to guess around 2600 pounds per hour per engine ?

According to the last report, FF maintained for the last 40 sec was twice that amount for each engine, which must not be far from a typical FF in order to maintain the G/S and cross the threshold at 50ft ?
I know someone said earlier the approach was quite bumpy with thrust variations, but in the same time, at this stage, BA38 was pretty light.

I would consider an airplane touches down in such a low energy situation 1000ft before threshold in case of dual engines flame out ... but I find it too much when each FF was between 5 and 6000 pounds per hour ?

Just a thought ...

[FullWings]

According to the last report, FF maintained for the last 40 sec was twice that amount for each engine, which must not be far from a typical FF in order to maintain the G/S and cross the threshold at 50ft ?
Unfortunately, far enough.

With F30 in calm conditions, you're going to need about 1.05-1.06EPR (c.50-55%N1) to maintain a 3deg slope, fully configured at Vref30+5, at the approximate landing weight we're talking about. The engines at the time were producing 1.02-1.03EPR from the AAIB report.

Things improve a bit with F25, needing 1.03-1.04EPR (45-50%N1), so pretty close, which is why moving to F25 might have helped. If the failure had occurred when the flaps were at 20 or less, the residual thrust would have been in the ballpark for maintaining a 3deg slope, gear down. That wasn't what happened, though.

[CONF iture]

Thanks for the helpful data FullWings.

I don’t want to sound picky, but to me, looking at the graph, the engines at the time were producing more like 1.03-1.04EPR, which is a bit closer to the desirable request.
Anyway, the point is there was still some valuable produced thrust, knowing that the FF reduced only 8000 feet before the threshold, I am surprised BA38 touched down at the end of the rope a full 2000 feet before the usual touchdown point ?

In no way this is a critic to the crew, but keeping the Vref would have been a better option than keeping the Glide Slope.

As we have seen again in CIA this week, dual engine malfunction (?) in final DO happen.
It would be time to implement such exercise in sim training, not to cover all possibilities but just to make aware of different options and consequences.
As always, let’s learn from the unlucky one.

[FullWings]

Hi CONF iture,

I took the EPR levels from page 2 of the most recent AAIB Interim Report, where it states: "...at a height of about 720ft the thrust of the right engine reduced to approximately 1.03 EPR (Engine Pressure Ratio); some seven seconds later the thrust on the left engine reduced to approximately 1.02 EPR" and further on in the same paragraph: "...The FMVs responded to this command and opened fully but with no appreciable change in the fuel flow to either engine."

...keeping the Vref would have been a better option than keeping the Glide Slope.
An interesting hypothesis. F30 on the 777 is the most you can hang out, i.e. it is drag flap with little corresponding increase in lift compared with F25. I would put forward that Vref30+5 is, with *significant* thrust being produced, quite a bit faster than Vx in this situation. Maintaining speed at 'bug' (1.3Vs+5) with F30 would lead to intersecting the ground plane some distance short: not a real improvement on what happened. There is the possibility of some help from ground effect but a) it's not over flat terrain and b) the aircraft is in its 'dirtiest' config. and bleeding energy fast. I don't think we'll ever know for sure what the optimal course of action might have been, unless someone runs some *very* detailed computer analyses (NOT in a simulator). I have a hunch that the answer will be different for each second that goes by on the approach.

It would be time to implement such exercise in sim training, not to cover all possibilities but just to make aware of different options and consequences.
I've done total engine failures as part of conversion/recurrent training on several types, including the 777. However, the situations have been (deliberately) set up to be 'survivable', i.e. a more than evens chance of getting the thing down on the runway in one piece, given average skill levels. The BA38 (and possibly the recent RYR) were both at the edge of the envelope and to try and train for rare incidents like these would probably leave the impression that in real life you'd be lucky if you weren't dead. A bit negative, not to mention the best recovery techniques are probably peculiar to each incident, so there is little 'generic' help to take away with you...

[PETTIFOGGER]

Phil gollin, [I think calling the AAIB suggestion a "theory" is a little bit too optimistic - they do not think there was enough water to form sufficient ice, and can't model a reasonable event to cause damage.

I think it is merely something they are investigating.

....and something that 2 of the 3 AAIB Safety Recommendations addressed. Concerning the semantics, "theory" seems appropriate as defined by the OED. On your comment about there being insufficient water to form ice, isn't that what I said?
Rgds

[phil gollin]

Pettifogger

A "theory" which fails to have the correct circumstances for it to be valid and also which cannot be even commenced to be tested is not a valid "theory".

.

[wilyflier]

Phil to reply to your assertion about not enough water content strikes me as "denial" ,The Met physistists swore there wasnt enough water at 25000ft to cause a Viscount complete 4 engine shut down over the Alps in1958. Their figures were out by an enormous factor , something like100/1. So we had to modify all Bristol Proteus engines as a result.
Heavy ice built up in the Ubend very rapidly,then came away in a rush

[PETTIFOGGER]

Phil gollin, re your post #2066, sorry to get picky or even pettifogging about this, but according to the compact OED, a theory is a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained. 2 an idea accounting for or justifying something.
http://www.askoxford.com/concise_oed/theory?view=uk, (http://http//www.askoxford.com/concise_oed/theory?view=uk)
or if you prefer Chambers ED "an explanation or system of anything: an exposition of abstract principles: speculation as opposed to practice". (sorry, no linked source for this one)
Or the Merriam-Webster dictionary "6 a: a hypothesis assumed for the sake of argument or investigation b: an unproved assumption". This one seems particularly fitting, wouldn't you say? theory - Definition from the Merriam-Webster Online Dictionary (http://www.merriam-webster.com/dictionary/theory .)

Sorry to be irritating and quote dictionary definitions, but "theory" as described above is what I meant to say, and it seems to me to be entirely appropriate at this stage of the investigation. If you or others think not, or disagree with some aspect of the AAIB's Interim Report and Safety Recommendations, I shall respect their views, but without seeing convincing arguments (or sources in the case of further 'definitions' of 'theory'), would be unlikely to agree with them. For the present, I prefer to stick with the AAIB's avenue of investigation, particularly the yet to be seen assessment of the fluid dynamics modelling, something which I alluded to much earlier, around post #500, I think.
rgds pf

[phil gollin]

This is a waste of time.

It is a hypothesis - as in "IF there were more water, then ......."

It cannot be a real "theory" as it doesn't have the right conditions to start with.

.

[gas path]

Nobody appears to have a definitive answer. That is the AAIB, Boeing, etc,etc. As has already been published the complete fuel manifolding, valves etc had been removed from one wing and reassembled into a test rig. Now (in the last week!) the complete manifolding from the other tank has been removed to make up the complete a/c assembly to see if that makes any difference to the test results.:8

[Green-dot]

@ wilyflier,
The Met physistists swore there wasnt enough water at 25000ft to cause a Viscount complete 4 engine shut down over the Alps in1958. Their figures were out by an enormous factor , something like100/1. So we had to modify all Bristol Proteus engines as a result.


Not to be nit-picking, to my knowledge the Bristol Proteus was indeed prone to icing but was married to the Britannia, not the Viscount. The Viscount had RR Darts.


@gas path,
Now (in the last week!) the complete manifolding from the other tank has been removed to make up the complete a/c assembly to see if that makes any difference to the test results.

With regards to "the other tank", that does not mean only the other main tank but I assume that also includes the fuel lines and override jettison pumps from the center tank?


Green-dot

[gas path]

With regards to "the other tank", that does not mean only the other main tank but I assume that also includes the fuel lines and override jettison pumps from the center tank?

Yes, that should have been tanks! So the (test) rig assembly will include everything on the fuel side.:8

[wilyflier]

Green dot post 2071
We all know the difference Viscount /Brit and Dart/Proteus but both engines were reverse (air)flow
The Viscount event was a wake up call.
My statement pointed out that the pundits figures on the water content conditions everyone accepted as normal were wildly wrong and so design changes were made across the industry.Reverse flow was avoided in new engine designs.Existing designs were modified to de- ice the bends.SOPs were issued to avoid icing conditions
It may be a bit fanciful but are we coming to the idea that liquids and gasses have similarities in flow behaviour round convoluted ducting and that ice accretion occurs in pipe lines carrying wet fuel similar to impact icing on wings and such? .New stricter parameters for dynamic fuel-icing avoidance?

[JW411]

wilyflier:

"We all know the difference Viscount/Brit and Dart/Proteus but both engines were reverse (air) flow".

In words of one syllable (or maybe two) - boll*cks.

The Proteus as fitted to the Britannia was indeed a reverse flow engine but the RR Dart was most certainly not.

For those of you who are unfamiliar with reverse flow turbo prop engines, here comes a simple explanation.

The only reason to have a reverse flow engine is to reduce the length of the engine and make it more compact (like the PT-6). So, the airflow enters the intake behind the prop and then goes through a 180 degree bend before entering the compressor. Then it goes through another 180 degrees before the combustion stage and then exiting through the turbine stage.

On the Britannia, the Proteus engines used to ice-up badly on the first U-bend and this caused the aircraft to be years and years late on entering service.

Even then, the problem was never satisfactorily solved. The civilian Brits had heating skins (B skins) fitted but their use caused a 10% loss in thrust. Even then, the engines were for ever shutting down and restarting (called "bumping") in icing conditions and this ensured that the crew never were allowed to go to sleep.

The RAF had a cowl heat system fitted but this resulted (so I'm told) in a 25% loss in thrust every time the system was used.

I will now move on to the RR Dart; I flew the Argosy for ten years and also the Viscount 802/806.

The Dart was a conventional engine in that there was no reversal of flow. It simply went: compression stage, combustion stage and then turbine stage. That is why the Dart was such a long and slim engine.

In fact, the engine was developed in a very simple fashion. When the Da 6 was not powerful enough, compression and turbine stages were added and so it was that the cowlings got longer right up to the Da 10.

I have never heard of four Darts failing at once through icing. I have personally had four inches of jagged ice on the engine intakes after an engine antice fault and not one of them even murmured.

[wilyflier]

Sorry about the bollocks ,Didnt the dart have a centrifugal stage whuch changed the direction of the airflow>?
As for the Viscounti icing up over Switzerland . Im not wrong about that .Caused plenty of kerfuffle at Bristol ,I was there

[Fzz]

This page (http://www.vickersviscount.net/Pages_Technical/Technical.aspx) has a cross section of a Dart.

[wilyflier]

Thanks Fzz, look like plenty of U bends there to me.

[CAAAD]

Dodgy Proteus U bend at inlet to compressor so cold.

Perfectly OK Dart U bends at compressor outlet so hot.

No mention of the Proteus Rabbit Warren fix yet!

[JW411]

Well, I suppose it is a matter of your interpretation, but I would hardly call a two-stage centrifugal compressor where the airflow moves from the front of the engine towards the rear "a reverse flow engine".

Anyway, none of this has anything to do with BA038 so I'm off out.

[whattimedoweland]

JetPhotos.Net Photo » G-VIIX (CN: 29966) British Airways Boeing 777-236(ER) by jetman41 (http://www.jetphotos.net/viewphoto.php?id=6417542)

[Green-dot]

whattimedoweland,

Nice flight deck picture.

Does anyone happen to have a picture of the BA B777 first class cabin (four class cabin configuration), preferrably taken from the rear in the direction of flight?

Thanks,
Green-dot

[Pontius]

preferrably taken from the rear in the direction of flight?


What, there's something behind the first class cabin :ooh:

(and there must be a few 'matron' comments regarding that quotation too :))

PS: regarding the 777 photo, what's Capt Cheapskate going to do now he's left his Holiday Inn pen behind:confused: Let's hope he got a new pen on his IAD nightstop :}.

[sky9]

Looking at the graphs in the AAIB report, it would appear to me that if the crew had brought the flaps up to 20 and and accepted a speed close to the F30 bug speed (i.e the go around speed) with the remaining residual thrust there would have been a very good chance of getting the aircraft down in one piece. ( I write this as a retired 767 capt so am not familiar with the 777).
This is not a reflection on the crew of the aircraft but a suggestion for the future, has anyone tried it in the sim?

[Green-dot]

Looking at the graphs in the AAIB report, it would appear to me that if the crew had brought the flaps up to 20 and and accepted a speed close to the F30 bug speed (i.e the go around speed) with the remaining residual thrust there would have been a very good chance of getting the aircraft down in one piece.


Under normal conditions, bringing the flaps up from 30 deg. to 20 deg. would take the engines out of approach idle (with thrustlevers at idle position and engine anti-ice off), reducing thrust to minimum idle.

Not sure if that factor would have influenced the circumstances on the already rollbacked engines in this accident. In other words, if it would have restricted the already limited fuel flow even more or not. Hard to tell as long as the cause of the restrictions has yet to be revealed.


Another recent rollback is under investigation:

NTSB investigates Heathrow-like Trent 800 engine issue (http://www.flightglobal.com/articles/2008/12/10/319956/ntsb-investigates-heathrow-like-trent-800-engine-issue.html)


Green-dot

[precept]

It may be quite important that professional pilots continue to follow this thread. Yes, the AAIB and the NTSB have published information which will probably lead to a conclusion.

It should be very important to all who seriously contribute to this network that vigilance is important.

What happened to BA038 has not been satisfactorily explained. The corrective action makes sense. Nevertheless, the entire aviation community who live at high altitudes, in cold temperatures, for extended periods of time need to follow this thread.

I trust the official investigation teams and the people who support them. I also know from almost 80 years of experience in my family that truth follows examination.

What happened to BA038 is unacceptable. Stay on this thread and contribute.

The AAIB and the NTSB, Boeing and RR are to be trusted. We are the people who make that trust valid. Keep this thread alive.

Tom

[misd-agin]

sky9 (http://www.pprune.org/members/7001-sky9)

Keeping Danny in Sandwiches

Join Date: May 1999
Location: UK
Posts: 961


Looking at the graphs in the AAIB report, it would appear to me that if the crew had brought the flaps up to 20 and and accepted a speed close to the F30 bug speed (i.e the go around speed) with the remaining residual thrust there would have been a very good chance of getting the aircraft down in one piece. ( I write this as a retired 767 capt so am not familiar with the 777).
This is not a reflection on the crew of the aircraft but a suggestion for the future, has anyone tried it in the sim?
http://static.pprune.org/images/statusicon/user_offline.gif http://static.pprune.org/images/buttons/report.gif (http://www.pprune.org/report.php?p=4563532)

Yes, you can make the runway in the sim.

Flaps 20 is half leading edge slats. Large drag reduction with small increase in approach/stall speed.

Residual thrust was greater than idle.

Slowing below Vref increases drag and decreases your glide performance.

We have 20/20 hindsight, crew had seconds to make the appropriate decisions.

[tankermytanker]

What happened to BA038 has not been satisfactorily explained. The corrective action makes sense. Nevertheless, the entire aviation community who live at high altitudes, in cold temperatures, for extended periods of time need to follow this thread.

Can someone please tell me, or show me the agencie's 'corrective action' recommendations?
Thanks,
Tank

[airfoilmod]

Some action was taken by some Carriers within 60 days, and was mostly procedural and related to fueling; one can surmise water checks, dumping and test schedules, etc.My understanding is each Line reacted individually according to SOPS and modifications to station procedures. I haven't seen hard copy, and you may not either, then again, you might. In any case, everything is on this thread, so don't ask me to direct you to it, happy reading.

(You fly 135's or sumthin else?)

AF

[precept]

See following URL re USA FAA action re BA038


Justia Regulation Tracker Airworthiness Directives: Boeing Model 777-200 and -300 Series Airplanes Equipped with Rolls-Royce Model RB211-TRENT 800 Series Engines, - Federal Aviation Administration - 52909?52911 [E8?21138] (http://regulations.justia.com/view/120567/)

[Bis47]

Hello!


The investigation determined that over a long period of low power fuel flows and low fuel temperatures associated with cruise flight, ice can accumulate in the main tank fuel feed system and then release as a result of increased fuel flow when high thrust is commanded.


and later :


We have determined that the loss of engine thrust was likely due to ice accumulating in the main tank fuel feed system during long exposure to cold fuel temperatures and low power fuel flows. It is necessary to issue interim mitigating actions in order to prevent an additional accident.
Emphasis of mine.

Virtually identical ice release both sides, causing virtually identical fuel restrictions?

I have the feeling that they do issue an AD, for the shake of "doing something" ...

[airfoilmod]

You are on the money. However, the FAA is doing what it does, mitigate challenges to safe flight. Any AD is almost always a compromise, based on real world factors. One could fault the Trent design and suggest swapping out that powerplant for another less sensitive to corrupted fuel.
Holy CRAP, can you imagine? The Trent isn't the problem; in this case it is merely involved in the solution.

Initially, the carriers reacted by massaging their fueling and sourcing dependencies, including emphasizing steps on the book but not being followed.

Missing from the AD, quite naturally, is the politics and economics of yiping about the true culprit. Here is where I find fault with the FAA.

"In Spec.?" A spec isn't arbitrary, but it makes compromises in the real world. "Ice in Fuel?" Not cute, but how much is too much? The triple 7 is a brilliant aircraft, the Trent, like everything RR is an exquisite engineering feat. Chinese Fuel? The Jury is still out. My 2 pence. AF

Aside: If you are still worried about how ETOPS breaks down into a "simultaneous fault", don't be, myself and others have tried to point out that a twin op ends up functioning in unity with late stage homogeneous systems. Making "identical" demands of two engines (autothrottles) operating in a wickedly similar ambient environment produces wickedly similar results, not rocket science. Sometimes, ETOPS isn't. That can't be AD'd. ETOPS solution? One Trent, one GE per a/c. Better solution? get the water out of the Fuel.

AF

[DC-ATE]

"ETOPS solution? One Trent, one GE per a/c. Better solution? get the water out of the Fuel."

My solution: FOUR engines over water, period.

[airfoilmod]

Four engines over water, period? That's what I thought when ETOPS hit the pilot lounge, and I reacted the same way. I was made to feel like a reactionary and dinosaur. But that was also when four engines meant four hot pipes, loud flow through a single orifice. What calms my psyche when I fly twins over the Pacific these days, is that I'm flying two hyper dependable propellor engines. Basically, (very basically) ducted thrust turbo-props. I'm still a prop guy at heart, so call me old fashioned.

I'm not so sure Al wouldn't have preferred to have been flying over water when #2 exploded over Sioux City. Forced landings are exceedingly rare.

[DC-ATE]

"Forced landings are exceedingly rare."

Ya.....but it only takes ONE !!!

[airfoilmod]

It only takes one. For what? I've had three, all involved still breathing and still flying. The DC-10 fireball at Indiana was survived by many. It had three engines, was flying over a number of suitable asphalt runways, was not ETOPS, (E-THROPS?) and yet 180 people perished. An uncontained Turbine failure. The old arguments were mooted long, long ago. Fuel? That can be a problem anytime. Simultaneous failure? likewise. I will emphatically agree that loss of two engines in ETOPS is doodoo land. It is also a forced landing in a four engined a/c, generally. Think about it. It is certainly a forced landing in a three engined a/c. AF

[DC-ATE]

"It only takes one. For what? I've had three, all involved still breathing and still flying. The DC-10 fireball at Indiana was survived by many. It had three engines, was flying over a number of suitable asphalt runways, was not ETOPS, (E-THROPS?) and yet 180 people perished. An uncontained Turbine failure."

It only takes one forced landing to ruin your day.

You've had THREE?!?! I'd be buying lottery tickets if I was you.

Are you talking about the UAL in IOWA (not Indiana)? That was kinda "close to home" (same company) so to speak.

[sky9]

misd-agin
We have 20/20 hindsight, crew had seconds to make the appropriate decisions.

I wasn't making any criticism of the crew, the incident was outside the knowledge of the crew and therefore they cannot be criticised for what they did. I was however asking if there was anything that could be learnt from the incident for the future.

[airfoilmod]

Yes Iowa. Sorry. I think a forced landing has to do with an immediate and unavoidable landing, not whether it is survivable or not, and I don't think three of those is unusual in 40 years of flying. Without looking it up, I think it was Capt. Al Haines? Lots of help in the cockpit, and although the a/c was unflyable, people lived. The accident was powerplant related, the a/c had three engines (at least at T/O), and I think is instructive when discussing the "dangers" of ETOPS. By the way, I've always been fond of Douglas a/c, and if you fly (flew) the friendly skies, you remember my favorite, the DC-6. We may have some mutual acquaintances. AF

[atakacs]

I wasn't making any criticism of the crew, the incident was outside the knowledge of the crew and therefore they cannot be criticised for what they did. I was however asking if there was anything that could be learnt from the incident for the future.

Yep - being lucky can make you an hero...

Again they certainly did their best but the BA public relation coup (http://www.pprune.org/rumours-news/334267-ba038-crew-get-ba-safety-medal.html#post4233069) is really mind boggling :(

[DC-ATE]

"Yes Iowa. Sorry. I think a forced landing has to do with an immediate and unavoidable landing, not whether it is survivable or not, and I don't think three of those is unusual in 40 years of flying. Without looking it up, I think it was Capt. Al Haines? Lots of help in the cockpit, and although the a/c was unflyable, people lived. The accident was powerplant related, the a/c had three engines (at least at T/O), and I think is instructive when discussing the "dangers" of ETOPS. By the way, I've always been fond of Douglas a/c, and if you fly (flew) the friendly skies, you remember my favorite, the DC-6. We may have some mutual acquaintances. AF"

Yes, it was Al. Are you saying HE had three forced landings, or you? I'm just thankful I never had ANY in 30 years.

Ah yes, the DC-6/7. First Type Rating. Great machine. Flew all seats. I was the last one off. I still prefer the Connie, but never got a rating in it. Probably why I liked the -8 so much; some similarities with the Connie.

Yup, we probably have some mutuals. I guess we're getting a little off course, however.

[precept]

This is a pro-forma entry.

Given no futher input from AAIB, NTSB, FAA or other authorities from 14 January 2009 regarding this thread, the members continue to await further science and knowledge.

The BA038 accident remains a serious and unacceptable situation. It is hoped the interim action required by the AD note eliminates the possibility for further issues.

Nevertheless, unresolved causes for accidents and appropriate final correcctive action must be the primary focus of this thread.

[airfoilmod]

I'd have thought a better approach would have been an "FD". Fuelworthiness Directive, and aimed at the fuel producers, not the a/c and operators. "Ice can form and block passageways, preventing increased flow....etc." Curiouser and curiouser. L. Carroll would have smiled.

AF

[thinkingpilot]

hello people!!!!!!!!!one year .....airline /engine/location of crash /investigating authority all from the same country !no result when ALL the data is available. ??? sorry but wheras i have the greatest of respect for british proffessionalism this is a cover up and i am surrprised that more people dont care :ugh:

[1000 to go]

Certainly a cover up in my view. Convienient that any of the alledged ice would have melted pretty quickly. There is no other explanation.

[M.Mouse]

Utter rubbish.

It can take a good deal longer than a year to publish the final report. Why does everybody see a conspiracy in everything these days?

Personally, I trust the AAIB.

[airfoilmod]

Missing the point maybe? Accomodating ice in fuel is irresponsible and negligent. The FAA has blundered utterly. "Ice in your fuel? Here's how, mate".

[wiggy]

In this era of 24 hour rolling news and instant messaging it seems everytime a professional agency carries out an investigation in a careful controlled and considered manner there are screams of "cover up" or "conspiracy". Just to be clear The AAIB have a very good idea what happened but are not yet ready for it's findings to be published in "The Sun" or "Daily Mail".

In the meantime many those who really need to know have been briefed as to the ongoing state of the investigation and more importantly all of those who really need to know have been briefed on the preventative procedures that need to be followed to prevent a repeat of the 38.

Those of you who don't need to know are going to have to put up with "Dancing on Ice" or "I'm a Celebrity, Get me out of here" if you want instant gratification.

[lomapaseo]

all of those who really need to know have been briefed on the preventative procedures that need to be followed to prevent a repeat of the 38.

Those of you who don't need to know are going to have to put up with "Dancing on Ice" or "I'm a Celebrity, Get me out of here" if you want instant gratification.

Actually Pprune has adequately briefed those capable of understanding. The problem that is left is that many readers not that close to the subject want a formal report to state a conclusion where it can be pointed to. For that they will have to wait.

[phil gollin]

Quote :

"..... In the meantime many those who really need to know have been briefed as to the ongoing state of the investigation and more importantly all of those who really need to know have been briefed on the preventative procedures that need to be followed to prevent a repeat of the 38. ......"

unquote


Really, how fascinating - I'm sure you don't mean the FAA Airworthiness Directive which is nothing more than a bit of common sense on top of guesswork - which has no basis on known facts. It goes along with the hypothesis that IF there were more ice than thought possible AND there was an unexplained amazing set of circumstances that meant both sides fuel systems acted separately, yet almost simultaneously and to the same extent - then the AD makes perfect sense.

As a piece of common sense the AD is good, but no one can be sure it is a proper preventative.

.

[Green-dot]

Convienient that any of the alledged ice would have melted pretty quickly. There is no other explanation.



If so, evidence of this would have been found somewhere in the engine feed lines, FOHEs or fuel filters in the fuel delivery system, which according to the AAIB reports released sofar, is not the case.

To quote the September 2008 report:
The samples from engine fuel filters and housings contained a small number of very small droplets of water. These droplets could have resulted from the ingress of fire fighting media through damaged engine components, or might have been free water, which naturally settles in this area.

No cover up, just lack of evidence to prove one (ice) of perhaps several possible hypotheses. It takes what it takes to come to the right conclusion. The final report will most likely not be released some time soon.

[wiggy]

You are absolutely right, I don't mean the FAA Airworthiness Directive.

[RomeoTangoFoxtrotMike]

Ba 038
This is a pro-forma entry.

Given no futher input from AAIB, NTSB, FAA or other authorities from 14 January 2009 regarding this thread, the members continue to await further science and knowledge.

The BA038 accident remains a serious and unacceptable situation. It is hoped the interim action required by the AD note eliminates the possibility for further issues.

Nevertheless, unresolved causes for accidents and appropriate final correcctive action must be the primary focus of this thread.
Sigh....


Originally Posted by Viking101
So when is the official report of the accident coming out?

Lets have some experts from the NTSB (or eq in UK) stating the problem, although I am bearing in mind all your tech knowledge and interesting speculations and rumours

Feels it has been too long now... Someone trying to hide anything maybe? Or just hoping that people "forget" about the whole thing? Yay- more speculations
If you had been paying attention, you would have seen posts 852 and 1006, where I note:-

"I've just crunched the data on published formal reports by the AAIB back to 2006... The average length of time from incident to final report publication is 25.6 months, i.e. a little over two years. This does not and has not stopped them issuing recommendations, where appropriate, before the final report."


See this post (http://www.pprune.org/rumours-news/340666-ba038-b777-thread-85.html#post4368543)

[phil gollin]

Well ....... I suppose an "happy" anniversary is in order (?)


Quite a coincidence another no power landing in a city - but at least those circumstances seem to be known.

.

[CONF iture]

Question :
Is there anything written in the BA collective agreement for the concerned pilots to get a copy of the data not ASAP but as soon as Available, in other words not later than the AAIB ?

[Carnage Matey!]

Thats an easy one to answer. No.

[timbob]

I agree with previous post that fuel suppliers/producers should be a point of focus. This flight was from Bejing, very light passenger load, and obviously parked at high altitude for a considerable time. I remember a bulletin issued to pilots and dispatchers at my old airline that forbade the use of polar routes to North America, due to the lower quality fuel available in China, Bejing in particular. We routed over central Siberia and Alaska without incident (B-777's) but no further north. Evidently lab tests conducted on some fuel samples from China revealed a variation in fuel freeze points that was disturbing (at the time).

[airfoilmod]

The AD (per se) is a step not taken lightly by the FAA and its supplicants. Where is the usual grumbling? Fuel Burn, grumble grumble. Workload issues, grumble grumble, Training costs, grumble grumble. I think crews were (have been all along) cognizant of the hazards. This smells of dancing around the issue, political correctness, what have you. The Trent may have "weak links" that only show when water is in fuel. Is this on the Trent? NO, on the fuel side, in my opinion. I guess the FAA stopped short of demanding a different F/O heat exchanger (for example), but what remains is a tacit forbearance of ignorance of what has up to now been strict guidelines surrounding fuel composition, transport, storage and oversight.

AF

[Carnage Matey!]

The investigation has already shown the Chinese fuel was well above specification. What the investigation is currently showing is that a lot of what we think we know about the behaviour of water in fuel is wrong.

[airfoilmod]

Point taken. However keep in mind "above" spec. is not necessarily "on spec." There is no "better than spec." There is spec. "met" or not. What you suggest may be unknown water behavior in fuel may be a result of not in spite of "above spec."

AF

[Carnage Matey!]

Well in the case of the Chinese fuel the spec was met and exceeded by a considerable margin. The current testing is being conducted on fuels fro a variety of sources and it's all showing the interesting behaviour regarding water content.

[M.Mouse]

Carnage Matey, will you stop introducing facts into this thread, it upsets the armchair experts.

Thank you.

[airfoilmod]

Would you explain your vague terms? "Exceeded"? "From several sources"?

Because if you are suggesting the Fuel is surprising people, you are also suggesting the Trent has an anomalous "fuel problem".

Be specific, explain your statement, err, "fact", ( for Mr Mouse., and the rest of us).

See, the problem appeared to be specific to the Trent 800, has it expanded into other types? You see where you're going?

AF

[Carnage Matey!]

OK, specifically for the semantics game, the fuel freeze point for the Chinese fuel was colder than required for specification, the water content was lower than the permissible maximum. In that way it exceeded spec. There's no problem talking about something exceeding spec. Every engineering organisation I've worked in (and thats quite a few) has had no issue with describing something as exceeding spec. Nonetheless talk about exceeding spec is a pointless word game and all this could all have been gleaned from earlier posts.

The behaviour exhibited by water molecules in very cold fuel is not as expected and investigations are ongoing to establish what mechanisms and behaviours are at work. The Trent 800 is the only engine being investigated initially and it would appear that specific interactions could exist between the fuel/water mixture and elements of the Trent fuel feed system that could lead to unexpected ice accretion. Boeing intend to test the entire 777 fuel system to see if the fault could occur elsewhere in the system. Given that the unexpected fuel/water mix behaviour will be common across all aircraft operating in similar environmental conditions it's quite plausible other aircraft types could be affected.

[airfoilmod]

And it is "expected" the fuel problem "will be" common across all other a/c operating in similar environment? The semantic problem isn't mine, sir.

You describe Boeing's "intention" to test the 777 fuel system. When will that happen? After another year?

Please look at your last sentence. This is not the verbiage of science.

"It's quite plausible that other a/c types will be affected?"(italics mine).

It sounds like a reporter with an agenda.

[Pinkman]

When CM says 'exceeded' he means, in the case of freezing point, that it wasn't just ' - 47 deg C' (the usual spec of jet A-1) because it was in fact RP-3/Jet Fuel Number 3 which is what is sold as equivalent to Jet A-1 in the Chinese market. There is indeed a common phrase "meets or exceeds" spec in our business so you are wrong about that although from a fit for purpose / contractual point of view, yes, it either meets spec or it doesnt. It did. By miles.

What he has also said or implied is that the detailed research is discovering some heretofore unknown relationships between fuel composition and extended exposure to extremely low temperatures.

Given the fact that Chinese Jet is probably wide cut, that is of no surprise to me, and although I am nowhere near the investigation it also wouldnt surprise me if there were to be discovered that there were a physico-chemical interaction between wax from wide-cut product (similar to diesel in winter) and microscopic ice crystals under these conditions. Its a personal guess, and I would bet my house on it, but it will be something like that.

I cant see that he is at all suggesting the Trent has an anomalous "fuel problem", although if you ran RR Trent and GE 90 together under identical conditions it would be unlikely that they would both respond identically. One would inevitably be slightly more sensitive than the other to low temperatures and variations in certain fuel components and on the basis of one incident you couldnt say which.

What he didnt say and what it WILL do is to introduce an additional and/or an altered test for freeze point and maybe introduce additional tests or change the upper limit on aromatics or density, and possibly some other parameters. Now that I would bet my house on.

Pinkman

[airfoilmod]

Noted. However, the implication is the fuel is "better" than spec. OK.
Then where is the problem? The spec? or the fuel/Trent lnterface. If other systems are not being tested, where is the "new" or "surprising" data. Either the Fuel effects are singular to the Trent, or NOT. If singular to the Trent, whose "problem" is it? Suggesting a new and mysterious chemical profile for Jet Fuel is irresponsible. One CANNOT have it both ways. Bad Fuel? Trent/Fuel interaction?

Pinkman- "meets or exceeds spec." though old, and tried, implies a "value" and to me doesn't belong in a description of Fuel. One wonders how the FP is "exceeded? What mechanism? Lights? Melamine?

AF

[Carnage Matey!]

Are you a fan of 'Loose Change' Airfoilmod? If you are going to quote me at least do it accurately. I said:

Given that the unexpected fuel/water mix behaviour will be common across all aircraft operating in similar environmental conditions it's quite plausible other aircraft types could be affected.


I did not say:

it is "expected" the fuel problem "will be" common across all other a/c operating in similar environment


My statement is a simple logical conclusion that if we are discovering a new interaction between fuel and water then as all aircraft use fuel (with some water in it) then all aircraft could be affected. There's nothing contentious in that unless you are looking for some sort of conspiracy theory.

As for the Trent/fuel interface issue, the Trent is the only engine under close scrutiny as this is, I remind you, an accident investigation on a Trent powered aircraft. If unusual behaviour is noted in the Trent no doubt subsequent tests will be performed on other engine models, but first you need to know what to test for and that is what the investigation is trying to establish.

Boeing will get round to testing the fuel system just as soon as they can finish building the full scale 777 fuel system inside a large vacuum chamber that can create and sustain temperatures of -73C and lower for a prolonged period at low atmospheric pressure. That sort of kit doesn't get built overnight.

There's no question of bad fuel, just that we don't know as much about good fuel as we thought we did.

[airfoilmod]

Appreciate the patient reply. Let me try a different course, I seem to be having difficulty with language.

You suggest the Trent is being singled out for testing because it was fitted to the accident a/c. Also that Boeing will follow up by testing the 777' complete system by way of mockup, to eliminate (or implicate) the airframe.

I do see your point that the Trent is not being impugned to now. What is alarming to me, (taking as fact your statements re: FP/Fuel), is that there is a new horizon of unexplored chemistry re: FUEL. This is disconcerting, since I fly alot and frequently on ETOPS cert. a/c. That Boeing hasn't finished their mockup, and other engines are not being tested, my assumption is that either the Trent or the Fuel is drawing most suspicion, or the several investigative bodies are being rather careless with conclusions needed on a more timely basis.

Are Chemists that expensive? Forensic Metallurgists? I'll help pay. As will all who fly.

[Carnage Matey!]

I'm afraid you are going to have to be more patient airfoilmod. Given that this is the only known incidence of this phenomena occurring in service I think the odds are on your side next time you fly. Temporary measures have been taken to minimise the chances of a repetition.

Unfortunately it's just not as simple as saying it must be the fuel or it must be the Trent. It could be both. The fuel clearly is introducing the contaminant (water) into the system. The question is why does it form ice accretions? Do these form only because of the fluid dynamics in the Trent system? Do they form elsewhere in the 777 fuel system and only become trapped in the Trent because of it's design? Could this occur in other designs? Are there geometries which encourage ice accretion which are not specific to the Trent? At the moment all they can confirm is that in a certain part of the Trent ice can accrete under certain conditions, but given that nobody has tested any other engines like this nobody can say for sure whether other engines could be affected.

This is fairly blue-sky research and throwing money at it doesn't necessarily give you an answer any quicker. If it did we'd all be using our fusion reactors to power plants manufacturing an HIV vaccine.

[airfoilmod]

I try not to read too much of inference into web posts. It's useless. So.
You say the Rollback on 038 is the only incident of its type? Not so. Unless you mean the only one causing an accident.

If you "sense" impatience in my post, you are correct. I believe I share this with others who have posted on this thread. I draw my conclusions from what I read here.

Does this "new frontier" of Fuel chemistry concern you? While flying, I never got completely comfortable hearing ATC tell me: "Standby". Tell someone else, is what I was thinking. Not irrational, considering I was giving over my flight to another, if only temporarily. The same holds true here.

Long ago, I was downwind on first solo, abeam tower. "Cessna xxxJ extend downwind for Aztec landing straight in." 3 MILES later, I timidly called Tower requesting a base turn. Never been patient with other authorities since; at least not completely.

AF

Aside: by the way, could the reason no other engine types have been tested "yet" mean anything to you?

[airfoilmod]

you mention that in certain areas of the Trent ice can accrete? That is possible, but Captain Cargill claimed the ice formed first, before entering the Trent. I'm still assuming (among other assumptions) that the heat exchanger (Fuel/Oil) is the "pinch in the pipe". Tiresome, these bleats to "wait for the report". Of course; meanwhile I think discussion is allowed.

[Carnage Matey!]

If you mean the only rollback in which ice accretion is strongly suspected of being the cause then yes, I believe it is. Other than that I can't add any more. I'm not involved in the investigation and will have to wait for the report just like you.

[airfoilmod]

While we're waiting, I'm still interested in your statements that Fuel is behaving in ways hitherto unknown to the flying and chemistry community.
For obvious reasons, and I'm not winding anything, can you explain your post? M.Mouse called it the introduction of a FACT. Educate Me?

AF

[Carnage Matey!]

Like I said, I can't add any more. I don't know anything about the mechanisms at work, only that the behaviour is not as expected/predicted and they don't know why.

[airfoilmod]

You cannot add more? You make a statement that is frankly, wild and unsubstantiated, and you can't explain or quote sources?

You will excuse me if I take exception to your posts and to Mr. Mouse's ill founded support.

Regards, AF

[FullWings]

AF,

I can sense your frustration (almost a disturbance in the Force) but there are many serious, lab-coat-wearing, possibly pipe-smoking engineers and scientists working on this problem and the ramifications thereof. I am told that the sum of available knowledge on fuel/water behaviour at different temperatures is not at the level that many expect it to be - there is an attempted remedy in progress. Please be patient.

Have you seen phase diagrams for plain H2O or Iron/Carbon? Amazing complexity for a pure chemical or simple mix; I wouldn't be surprised at all if some hitherto unseen weirdo behaviour of certain concentrations of water, hydrocarbons, temperature and pressure comes to light...

[Re-Heat]

AF

I see you are somewhat alarmed that it has been mentioned that we are dealing with hitherto potentially unknown properties of fuel. Regardless of what the AAIB and Boeing are currently investigating, you should perhaps instead think of the investigation as more of an intellectual investigation.

Not to detract from the seriousness of the incident last year, the key is that incidents such as that are now so rare, that the few accidents we do have are no longer caused by extremely obvious errors in piloting ability or build quality. It is natural that people will of course now work to reduce this risk as well, but you have to imagine this risk as miniscule in relation to all the others that have been dealt with over time in the past, and of more intellectual interest than of clear and present danger on ETOPS flights.

I try not to read too much of inference into web posts. It's useless. So. You say the Rollback on 038 is the only incident of its type? Not so. Unless you mean the only one causing an accident.
Under these circumstances, I believe that the AAIB and Boeing do not consider this event to have ever occurred at all before under these circumstances. Nor do they expect it to in the imminent future.

I understand that they think they know what caused it, that procedures have already been altered to minimise the risk, but that the exact, precise chain of events is hitherto still unknown.

We live in a modern world where everything is instant - there is a reason many of us are not research scientists, as we are not patient enough. There is however a place for the detailed and diligent work that those people are doign right now, and will be for some time on the problem that occured to the aircraft.

[airfoilmod]

Thank you, that was kind. I may have an off-course read on the science; I doubt it, but without updates, one is left with slim pickens. What is apparent, assuredly is my lack of Faith in the state of the authority vis-a-vis daily ops. The silence is speaking volumes. The pipe smokers will never change, that's a good thing for the most part. The change that is needed is a posture of willingness to disseminate results and show at least a feigned interest in safety and a shoring up of consumer confidence, by communicating with the client. The industry is wicked safe, but the bureaucratic nonsense of the authority is maddening and does little to add to the perception of safety among those who fly and couldn't care less about cascading nucleation.

And thanks to ReHeat.

AF

[Machaca]

"meets or exceeds spec." though old, and tried, implies a "value" and to me doesn't belong in a description of Fuel. One wonders how the FP is "exceeded? What mechanism? Lights? Melamine?The composition of crude oil varies considerably by region and even batch.

There are several methods of refining crude oil into desired base products and removing much, but not all, of the undesirable compounds. Additives enhance the refined base products to ensure they will perform to established specifications.

There are dozens of specifications for each product -- some are maximum limits, some are minimum limits, and some are range limits. The resultant finished products meet or exceed specs, yet still vary by region, batch, process and additives.

[Carnage Matey!]

My statements were neither wild nor unsubstantiated. I suspect Full Wings is getting his information from very similar sources to me, none of which are worthy of quoting because none are directly involved in the investigation. They get updates from the AAIB as a courtesy as the operators of the accident aircraft. Furthermore there's nothing in my postings regarding the fuel which couldn't reasonably be deduced from the information already in the public domain by anyone with a reasonable level of scientific competence. If you find the slow release of information from the investigative authorities frustrating then I'm afraid it's just tough luck. Investigation is not a process best served by a daily news bulletin or an hourly update on Twitter and nothing you or I do is going to change that.

[airfoilmod]

Had you offered a source of what seemed a rumour, that would have been satisfactory. Nobody appreciates the coy one when discussing serious matters. Just my opinion.

[FullWings]

AF,

Several of the posters on this thread probably a) fly for BA, b) are in or know Management c), have contacts in the AAIB/NTSB/RR (or are employed by one of these organisations), d) have a personal interest in the outcome of any investigations or a combination of all of these. They are probably also keenly aware of the media interest in this event and do not want to publicise things that may be confidential at this time unless explained in the most general terms.

I don't think a request for detailed references will provide much at the moment... Sorry.

[PETTIFOGGER]

airfoilmod,
See my post #1689 of 2 September.
rgds

[HarryMann]

Flipping back to that page I also notice my response to Viking soon after...

Feels it has been too long now... Someone trying to hide anything maybe? Or just hoping that people "forget" about the whole thing? Yay- more speculations
A Professional forum like this is really no place for puerile conspiracy theories... please desist.

Imagine if I looked further I'd see a wrap on the knuckles for that, :ouch:

[phil gollin]

When people say that boeing are "testing the Trent" I PRESUME what they mean is that they are testing the pipework arrangements associated with the Trent type of installation as the engine per se isn't (???????) at fault but its fuel feed, system. I remember from very much earlier in the thread that the Trent and GE pipework set up varies in various details.

When the AAIB and Boeing comes up with some solution to the Trent set-up then whilst that might be worth it JUST for the Trent 777s, it won't really be a full solution until the results can be extended into all aircraft and engine types.

AS AN UNINFORMED person I still find two things troubling ;

- 1: People still seem to be talking about "ice" whereas the initial reports, etc.... all SEEM to say there is insufficient water to cause the problem, so something else ("waxing" or a. n. other) might be involved. Can anyone clarify ?

- 2: IF whatever is eventually found to be the cause is a icing and/or "waxing" or whatever problem, I still find the almost simultaneous and exactly the same occurances in two separate systems amazing.

and lastly, I will be fascinating to see what the eventual fuel spec will say (or whether they will set different flight profiles for different aircraft).

.

[Bis47]

The recent AD seems to admit that similar (very similar) fuel feed troubles might happen, and so they recommend some preventive actions.

Authorities keep silent about one information and one procedure that might have saved the day, and according to the hypothesis of trouble reccurence, would as well save other flights in the future.

The information : best glide speed (or AOA) in different configuration (landing config, approach config ...)

The procedure : permissible cleanup actions as required in such dramatical circumstances.

In the las 12 months, we learned that multiple engine failures are not as exceptionnal as we think ...

Perhaps less exceptionnal than a single engine failure right at V1, on a limited runway ...

[misd-agin]

Best glide speed is published in dual engine flameout checklist for other Boeing products.

Flying 101, slow flight, is that the slower you go, beyond a certain point, the more power you need to overcome the drag. Configured that point is about Vref.

[misd-agin]

Accidents often advance knowledge. TWA 800 resulted in additional testing that uncovered more knowledge about fuel tank heating, and unknown localized hot spots, in fuel tanks.

We shouldn't be surprised if BA038 uncovers new knowledge about fuel either. The real world can be different than the best lab.

[FullWings]

Flying 101, slow flight, is that the slower you go, beyond a certain point, the more power you need to overcome the drag.
Definitely.
Configured that point is about Vref.
Hmm. That's an interesting proposition. Vref is an artificial construction ranging from about 1.2 to 1.3Vs in airliners - if it happened to be the best gliding speed in a particular airframe that would be by accident rather than design. In many jet aircraft, the last stage(s) of flap are there to add drag so the approach can be stabilised; this has the effect of increasing the curvature of the 'polar' and so bring Vs,Vx & Vy closer to each other. Having the gear down doesn't help, either.

I think most advice about gliding powered aircraft is written assuming a clean configuration... The wheels/flaps only come out when a landing is assured and you need to lose some energy. A 777 gear down, F30, Vref and no power I'd reckon you'd be lucky to get 7:1 out of it, rather than the 19:1 you need for a 3deg glide.

[misd-agin]

Fullwings - question was posed to engineer that has access to the L/D data for different configurations - "Vapp (Vref+5) is close enough to not worry about the difference."

I don't have the exact data, just the word of an expert.

This could be researched in a sim. Level flight(to increase fuel flow/N1's, and flight test various speeds and configurations. Lowest power required wins.

1.2 Vso? Have to double check my manuals but I think we always have 1.3Vso protection on arrival, 1.2Vso protection on departure.

Best glide is for clean(ie, best glide configuration). Agree that configurated would be much worse. If my math is correct BA038 did 6:1 at Vref -27 kts. I'll see if I can figure out glide ratio closer to Vapp in my next sim session.

[M.Mouse]

You will excuse me if I take exception to your posts and to Mr. Mouse's ill founded support.

Feel free.

I know what I know, you choose to accept or dismiss it as you see fit. Because you do not like not knowing is not really my problem or even of any interest.

[PETTIFOGGER]

Phil gollin,
See my post 1689 of 2 September. What follows is speculation, but consider this. Boeing, RR and the AAIB realized that there was not enough water to produce a sufficient quantity of ice to restrict that fuel to the engines and concluded that other factors were in play. They may suspect or have discovered after carrying out CFD modelling, that the fuel they are analyzing has exhibited non-Newtonian properties at certain temperatures. Examples of non-Newtonian fluids (also known as complex fluids) are blood, paint, egg white, and many other sticky fluids. The nature of these complex fluids is known, but their properties and the changes they undergo are difficult to predict when it comes to transporting them in pipes. Not too much is known about the effect of temperature, the onset of turbulent flow, and the propensity for agglutination of these complex fluids.
Regular jet fuel is a Newtonian fluid, as is water and other simple small molecule fluids. Perhaps the “exceeded spec.” fuel with a superior freezing point, displays non-Newtonian properties at certain temperatures depending on the architecture of the fuel delivery system? But this is idle speculation and largely a waste of time (as I think you said before) until we have more facts.

[Rightbase]

misd-agin writes:

This could be researched in a sim.

How would this tell us more than we (or the programmers of the sim) already know from the flight dynamics model programmed into the simulator?

Presumably the flight tests that validated the simulator model already have all this information.

[relax737]

A Professional forum like this is really no place for puerile conspiracy theories... please desist.

Imagine if I looked further I'd see a wrap on the knuckles for that,

Harry Mann, don't get too precious about it; this may be a professional forum, but the title of the site is Professional Pilots Rumour Network!!

And whilst a small point, it is a 'rap' over the knucles unless you have a roll of brown paper, or any colour paper for that matter.

[Tediek]

What is happening with the aircraft. I have seen it a few times now at LHR behind some fencing and without the vertical tail vin.

[Dairyground]

We are told that the proportion of water in the fuel was too low for significant quantities of ice crystals to form in the bulk fuel in the tanks or in the bore of the pipework. But could some water have frozen out on the insides of the pipes themselves, in much the same way that water from fairly dry air builds up ice deposits over time on the cold plates of domestic fridges and freezers?

Any ice deposited in that way would probably be fairly soft and easily detached to clog up the FOHE by increased fuel flow as thrust was increased.

[Pinkman]

....that the fuel recovered was entirely representative of the bulk fuel loaded. If fuel stratification occurred, it is possible that the fuel that was being consumed in the hours before TOD was much higher in water content than the average water content in the fuel as a whole when loaded.

The theory has already been advanced in PPrune that in a steady-state (cruise) condition the ice accreting on the face of the FOHE was removed at a rate equal to its deposition and that it was only when the flow dropped during descent that the equilibrium changed (despite higher OAT) and ice buildup began. When the aircraft piled in, the remaining fuel that didnt leak de-stratified and the ice remixed as dissolved water, and the ice that built up in transit from wing to engine dropped out mainly as free water (because the concentration of water to fuel was higher in the lines) ("ingress of fire fighting foam" doesnt do it for me). Because the proportion of water consumed during the flight was higher than that in the bulk of the fuel loaded, it follows that the concentration of water in the remaining bulk fuel at the end of the flight - into which the ice redissolved - would be less.

IF, repeat IF you accept that buildup model, then you also have to accept that it is possible that the water content of the fuel sampled at end of journey may not have been the same as that loaded prior to departure and that the water content in the fuel delivered to the FOHE was not homogenous during the flight.

Anyone who has experience of returning to a frozen Margarita on a hot day after an extended potty break knows what I am suggesting.

Pinkman

[Joetom]

Of interest.

Refuel two aircraft at the same time with the same fuel.

Action fuel/water drainage checks at 2/3 hours on one and do the other at 9/10 hours, results will tend to be different, more water will normally be recovered at the 9/10 hours checks.

After a long smooth cruise could guess results would be the same.

But now think the 777RR have new drills for crew to incease fuel flow to deal with the poss of water build up.

[phil gollin]

Quote :

....... But now think the 777RR have new drills for crew to incease fuel flow to deal with the poss of water build up.

unquote


IF there is either a water in fuel or fuel behaviour problem then ALL aircraft types will need to be re-examined. It MAY be that some aircraft have set-ups which mean addiditional measures are needed
- but ALL will need to be looked at.

.

[PETTIFOGGER]

IF there is either a water in fuel or fuel behaviour problem then ALL aircraft types will need to be re-examined. It MAY be that some aircraft have set-ups which mean addiditional measures are needed
- but ALL will need to be looked at.

- as the AAIB noted some time ago in Safety Rec 2008-49, page 20 of their interim report on G-YMMM.

[lomapaseo]

I copied this out of CAPTDOUG's thread DAL rollback update Trent895

DAL rollback update/Trent895

--------------------------------------------------------------------------------

SUBJECT: 777-200/Trent 895 N862DA Thrust Rollback During Cruise - 26
November 2008


-------------------------------------------------------------------------------
UPDATE 1 UPDATE 1 UPDATE 1 UPDATE 1
-------------------------------------------------------------------------------

Reference a) provides Boeing's previous fleet communication of a 777-200
with Trent 895 engines that experienced an uncommanded thrust rollback on
one engine while in level flight cruise at FL 390. The thrust rolled back
to a level above idle on that engine, approximately 40 minutes after a VNAV
step climb. The flight crew performed the Engine Response non-normal
checklist, which restored full capability to the engine for the remainder of
the flight. The other engine operated normally throughout the flight.

Based on the FDR data and the characteristics of the roll-back, it is
suspected that accumulation of water ice in the fuel path of the Fuel Oil
Heat Exchanger is the cause of the subject incident. Although the
circumstances are slightly different, the subject incident is believed to
have been caused by similar factors as those experienced in the 777-200ER
G-YMMM accident at London, Heathrow airport on 17 January 2008 as described
by Reference b).

Investigation Status
It should be emphasized that the investigations into both events are not yet
complete, with the G-YMMM accident under an open investigation by the UK
AAIB and the subject roll-back incident under an open investigation by the
US NTSB. Boeing, Rolls-Royce, the operators and other organizations are
supporting both investigations.

Recommended Operator Action
The circumstances of the subject thrust roll-back incident have led Boeing
to review the cold fuel operations procedures released by Reference c).
Based on this review, it is believed to be prudent to revise the interim
mitigating procedures to account for what was learned in the subject
roll-back incident. Changes to the interim procedures include:

Reduce the window at top of descent from 3 to 2 hours;
Assure the crossfeed valves are closed;
Assure minimum idle thrust for 30 seconds during initial descent, and;
Clarify the Condition statement in Engine Response Non-Normal Checklist
(NNC).

Reference d) provides a list of publications from Boeing that give the full
definition of the revised interim mitigating procedures. The FAA and EASA
are expected to release regulatory action to mandate use of the revised
procedures. These procedures are interim measures that will remain in place
until a permanent solution can be defined, tested, certified, and deployed
to the fleet.

Other Airframe/Engine Combinations
These interim mitigation procedures only apply to 777s powered by
Rolls-Royce Trent 800 engines and do not apply to other airframe/engine
combinations. Based on our knowledge of the system configurations, scenario
studies, and laboratory test results, we do not believe that immediate
action is necessary or warranted for 777s powered by other engine types or
non-777 airframes regardless of engine type.

Studies of the applicability of the thrust roll back circumstances to other
engine types and airframes are in work and will continue. Boeing will
notify operators of the results of those studies as appropriate.


Tom Dodt
Chief Engineer - Air Safety Investigation
The Boeing Company
Download this as a file

[airfoilmod]

A lot of surface area in a "small" volume. It fits previous conjecture. The design of the exchanger resembles a "filter", though not its intended purpose, other than as a heat sink; accumulations of small crystalline ice as suggested by Captain Cargill, to be "melted" by thrust augment sounds reasonable.

[Flight_Idle]

Regarding the melting of ice by the FOHE, it has been pointed out on this thread that sometimes hot oil is circulating, sometimes not as is required.

This must throw another spanner in the works, surely?

[airfoilmod]

I think the purpose of the Fuel/Oil Heat exchanger is to cool the engine oil with fuel on its way to the combustors. The spanner is the melting of water ice built up in the passages of the unit which then is injected and possibly quenches/prevents combustion.

The unit can be cooler than is planned for when long periods of exposure to high altitude temps and little power demand keep the oil cool and allows for ice build up in the HE. What hasn't been addressed adequately imho is the presence of water in the fuel. Unless we buy the explanation about some new and unpredicted science re: FUEL at low temp. (sic). Another possibility is the melting and REFREEZING of water, which then inhibits fuel flow to the engine. Relative difference in EPR ?

[Flight_Idle]

It is possible however unlikely that the hot oil/no hot oil in the heat exchanger, could be the very last hole in the swiss cheese?

I think there would have to be more than 5 liters of water to do it though.

I try to keep off this part of the forum, but I just couldn't resist my two penny worth!

[airfoilmod]

Five liters? I have no idea. lomapaseo ?

[Machaca]

Airfoilmod:

I think the purpose of the Fuel/Oil Heat exchanger is to cool the engine oil with fuel on its way to the combustors. Correct.

The spanner is the melting of water ice built up in the passages of the unit which then is injected and possibly quenches/prevents combustion.Wouldn't lead to cavitation. Perhaps the spanner is a mix: release of ice build-up in and/or before FOHE causes obstruction.

The unit can be cooler than is planned for when long periods of exposure to high altitude temps and little power demand keep the oil cool and allows for ice build up in the HE. Quite likely. And its position vs that of other powerplant mfg's.

What hasn't been addressed adequately imho is the presence of water in the fuel.As in the tested samples from BA038, or fuel in general?

[airfoilmod]

What could cause cavitation quite easily is a melting and Refreezing of ice crystals seriously necking down the flow, or even temporarily cutting it off completely.

Fuel in general: Storage, transport, transfer, etc.

BA038: sumping negligence, lack of critical procedure compliance
(Would apply to other carriers of course.)

There seems to be an unwillingness to address wet fuel other than spec measurement and an eagerness to eliminate contaminated supplies. Instead, the drill is "Undiscovered fuel characteristics, etc." at very low temp...

The Trent has an exposure here, vis a vis FOHE and other plumbing.



A very small amount of ice, perhaps present in barely nucleated crystals, could deposit over time in restricted flow areas. In other words, in spec fuel could cause serious flow issues, interfacing with a mechanical system that potentiates it. Follow on melting and refreeze would be indicative of such a concentration, though "in Spec."

I don't recall if anyone has brought up "downstream" cavitation.

[M.Mouse]

nucleated

What does that word mean, I cannot find it in either the UK or American dictionaries?

[MrBunker]

nu·cle·at·ed (nkl-td, ny-)
adj.
Having a nucleus or nuclei: the nucleated cell of a spermatozoon.

Hope that helps! Sadly, that's about as much as I can contribute to this runaway train of a thread. ;)

[stickyb]

What does that word mean, I cannot find it in either the UK or American dictionaries?

Just a few.....
nucleated droplet mechanism -- Britannica Online Encyclopedia (http://www.britannica.com/EBchecked/topic/421888/nucleated-droplet-mechanism)
nucleated - definition of nucleated in the Medical dictionary - by the Free Online Medical Dictionary, Thesaurus and Encyclopedia. (http://medical-dictionary.thefreedictionary.com/nucleated)
nucleated - Definition from the Merriam-Webster Online Dictionary (http://www.merriam-webster.com/dictionary/nucleated)
nucleated - definition of nucleated by the Free Online Dictionary, Thesaurus and Encyclopedia. (http://www.thefreedictionary.com/nucleated)

I really should stop digressing!!!!

[KitKat747]

It means granulated

[cockney steve]

As a non-professional, I hesitate to stick my nose in here,

The FOHE seems to be the fundamental difference in the two alternative power-plants.

The Trent would appear to have chilling problems, due to low flow of hot oil, when power demand is low.

Is it beyond reason to use an "electric blanket" type heater, thermostatically controlled, for those low-power, low fuel-flow situations when this fuel-icing becomes prevalant?

I appreciate there would be a substantial electric load involved, but the engine would have plenty of POTENTIAL power-reserve to cope, it being my understanding that the problem ONLY occurs when there is very low power demand in a very low ambient temperature..

another source of heat may be bleed-air?

or should I keep my nose out?

[TheShadow]

What's one plausible relationship between:

1. the incident below at bottom (which, according to latest ATSB revelations a few days ago, remains insoluble),
2. BA038 and
3. the A320 crash off Perpignan [Toulouse] (and maybe a few others)?
.

Answer:
The ability of water to free-flow migrate to different parts of a labyrinthine piped system, be it LP fuel or static air line - and coalesce into a static and blocking frozen mass, obstructing flow-rates and constricting sensor input data pick-offs. Think suddenly replacing engine oil with heavy duty grease.

Explanation:
A. When water is in solution in fuel or merely a frozen lump attached to a crevice in a tank, it's harmless. When water is free-flowing in a pneumatic static air pressure system all it does is slightly/imperceptibly dampen rates (ASI speed-changes, VSI, altimeters).

However when an icy lump dislodges due to fuel level changes, turbulence, warming, structural flexure etc, it can rapidly move, without any symptoms, to a position where it can critically obstruct flows.
.

B. When water in a static line moves to an area where it can freeze and obstruct ambient pressure changes from reaching sensitive transducers, then ADIRU data can become corrupted. This can happen suddenly and, courtesy of the software, produce abrupt and unexpected results. Think the difference between anti-skid braking on a slippery surface at 100knots - and simply selecting the parkbrake ON (at that speed).

The point being made is that the metamorphosis from free-flowing water to static and obstructionist ice-block is very capable of defeating system design software and producing sudden unexpected outcomes.
Not a lot is known about the behavior of water in a system of non-homogenous temperatures that is also subject to a wide range of flow-rates
.
When that metamorphosis is transitory and ephemeral, the phenomenon can be a difficult one to envisage, let alone replicate. It's the same problem with a wiring fire. Did the wiring flash-over and a fire cause the crash OR was all that burnt wiring just burnt in the post-crash fire?
.
Those of us ho have experienced the rapid confusing loss of flight instrumentation in the climb due to frozen pitot or stati lines will be ready converts to this theory. Those who went on to fly modern aircraft where the same systems can become flummoxed by such data corruptions would be less easily convinced - unless they were participants in the incidents mentioned (or similar). If you're not convinced about the effect that water can have upon a computer, I urge you to empty an ice-tray on your keyboard and stand back.
**************************************************

At 0932 local time (0132 UTC) on 7 October 2008, an Airbus A330-303 aircraft, registered VH-QPA, departed Singapore on a scheduled passenger transport service to Perth, Australia. On board the aircraft (operating as flight number QF72) were 303 passengers, nine cabin crew and three flight crew. At 1240:28, while the aircraft was cruising at 37,000 ft, the autopilot disconnected. That was accompanied by various aircraft system failure indications. At 1242:27, while the crew was evaluating the situation, the aircraft abruptly pitched nose-down. The aircraft reached a maximum pitch angle of about 8.4 degrees nose-down, and descended 650 ft during the event. After returning the aircraft to 37,000 ft, the crew commenced actions to deal with multiple failure messages. At 1245:08, the aircraft commenced a second uncommanded pitch-down event. The aircraft reached a maximum pitch angle of about 3.5 degrees nose-down, and descended about 400 ft during this second event.

At 1249, the crew made a PAN emergency broadcast to air traffic control, and requested a clearance to divert to and track direct to Learmonth. At 1254, after receiving advice from the cabin crew of several serious injuries, the crew declared a MAYDAY. The aircraft subsequently landed at Learmonth at 1350.

Currently available information indicates that one flight attendant and at least 13 passengers were seriously injured and many others experienced less serious injuries. Most of the injuries involved passengers who were seated without their seatbelts fastened. This constituted an accident under the ICAO definition outlined in Annex 13 to the Chicago Convention and as defined in the Transport Safety Investigation Act 2003.

Examination of flight data recorder information indicates that, at the time the autopilot disconnected, there was a fault with the inertial reference (IR) part of the air data inertial reference unit (ADIRU) number 1. From that time, there were many spikes in the recorded parameters from the air data reference (ADR) and IR parts of ADIRU 1. Two of the angle-of-attack spikes appear to have been associated with the uncommanded pitch-down movements of the aircraft.

Download complete report [PDF 1.2 MB (http://www.atsb.gov.au/publications/investigation_reports/2008/AAIR/pdf/AO2008070_prelim.pdf)]

[Flight Safety]

This Flight Global article is interesting. It explains the AD, and how the GE and PW FOHE installations are different from the Trent 895.

Boeing links Heathrow, Atlanta Trent 895 engine rollbacks (http://www.flightglobal.com/articles/2009/02/03/322023/boeing-links-heathrow-atlanta-trent-895-engine-rollbacks.html)

[airfoilmod]

What's becoming clear from this last release by Boeing is a possible genesis for the "behaviour hitherto unseen of Fuel".

Though in spec., fuel does have some content of water. It "freezes", but more along the lines of fine granules, that behave more like a "particulate" than a common picture of "Ice". As the "slurry" (my term) migrates through the fuel plumbing it can be deposited in a number of ways on surfaces and openings. Given time, this deposition can impede the flow. The added "pressure" of enhanced HP input may serve only to exacerbate the problem, perhaps dislodging deposits to be more occlusive downstream. Melting this "powdery plug" evidently solves the problem, interpreting the AD and its reference to PW and GE.So the fix is in modifying the geometry of the FOHE, its placement, capacity or orifices.

So Far.

[Flight Safety]

From the Flight Global article, it appears the GE and PW design recirculates some of the heated fuel back to the upstream face of the FOHE, thus preheating the new cold fuel approaching the upstream FOHE face (thus melting any water ice before reaching the FOHE). The Trent FOHE does not appear to have this warmed fuel recirculation feature, thus the fuel reaching the upstream face of the FOHE is colder than on the GE or PW designs.

[airfoilmod]

But I think there may be more to it. I don't think just cold temps are the culprit. I know I am inferring something here, but don't forget the additional plumbing in GE/PW in itself may be a bottleneck under certain circumstances. What's missing here is the "unseen characteristics" of fuel.
Now that may be some red Herring to "exonerate" the Trent, but I have to doubt it.

What hasn't been addressed as far as I know is the possibility that Fuel at very low temps, infused with some concentration of hard small "particle ice", may be behaving like a colloidal suspension rather than a homogeneous fluid. If that is so, centrifugal force, gravity and pressure would make Fuel behave like a "slurry". At certain shape and minimum size, a deposit of powdery water ice could cause all sorts of problems as it changes location, hardness, and size at will. Think "Plaque".

Just as most engines have a "bypass" for oil past its filtration, to continue flow, doesn't the Trent have an FOHE bypass? For Fuel? To avoid a plug and keep the injectors happy?

AF

[Flight Safety]

AF, if it did have the bypass, I suspect we wouldn't be discussing this accident.

[airfoilmod]

Rhetorical, my friend, bad sarcasm even.

[VFD]

I just question in the different return fuel routeing ahead of the FOHE on the GE and PW.

Had they experienced the iceing problem beforehand?
Was it just a convienent place to connect the return?

While sounding simple to reroute the return fuel ahead of the FOHE on the RR it will obviously take time to manufacture, fit and test parts involved to see if that will solve the problem.

VFD

[phil gollin]

I'm a little disturbed by Boeing's AD.

As a purely precautionary document - three cheers (but does it add to anything more than last Autumn's FAA one ?).

However, it seems a little too intrusive into the inquiries being undertaken by the proper authorities.

However, most importantly, there is no indication in the Boeing inturruption as to how the unknown process managed to affect two separate systems so similarly in time and effect.

Too much seems to be being read into something which is too vague.

.

[tanimbar]

Warning: I'm non-professional; not crew, not engineer - just scientist guest and thanks.

I suspect we are being given a lesson in global news management. I think it is a good and necessary lesson.

Investigators, Boeing and RR engineers etc. already know that the root cause of the BA038 incident is the state of the fuel in the tanks and pipes. For fuel temperatures below -18C the AAIB have stated,

"Below this temperature little is known about the properties of ice crystals in fuel and further research may be required to enable the aviation industry to more fully understand this behaviour."

Others here have agreed that the phrase 'little is known' is shocking. But, the industry cannot, and should not, allow that damning finding to be transmitted to the general public without first indicating that there are operational actions to hopefully avoid a recurrence, and a temporary engineering solution that can be retrofitted to a class of aircraft most susceptible to the problem, namely, Boeing 777s with RR engines.

Meanwhile, quietly, the industry concentrates its efforts on understanding what does happen to fuel on these long, high and cold flights and the more permanent solution to the globally pervasive problem.

This strategy is probably the only viable one to follow. I hope that the industry is actively trying to fill the hole in its knowledge, i.e. the behaviour of cold fuel.

I still think the fuel within the main tanks stratified in some form and that a pulse of "gloop", or slurry as Airfoilmod calls it (#2178), entered the delivery systems and partially blocked them.


Moving to tongue in cheek mode - Oh to be a fly-on-the-wall in the meeting room where RR are holding their forensic investigations into the decision stage on the FOHE design. Why that design, why not the GE or P&W one? Were the GE and P&W engineers just lucky or did they have knowledge that guided them, and if they did, was this available to RR? I've lots of follow-up questions but will spare you.

There is a lot to be learned about how the industry shares knowledge and, probably more crucially, the authorities must determine how it is that, this most technically advanced global industry, does not know how fuel behaves below -18C.

I'm still staggered by that.

Regards, Tanimbar

[airfoilmod]

The Press Release causes more problems than it solves, in my opinion. I am not expert in fluid dynamics by any stretch, but logic suggests the following.

It is highly unlikely there was liquid water any where in the fuel system of 038 for hours prior to the flight. If present as ice, then a "picture" of the state of the tankage would suggest that it was present as what? Cocktail ice? large blocks clinging to aluminum? That doesn't jive with the temps experienced by the a/c overnight or well prior to launch from Beijing. Block ice won't pump, and fuel won't "freeze" at all ambient temps. surrounding the flight. If the a/c brought it with on the flight in, that's one thing, but logic again suggests the problem arose on uplift in China. In spec. fuel would be carrying some quantity of water (as ice) in the uplifted batch.
As the flight progressed, this ice would "concentrate" in progressively greater quantities as it settled lower in the fuel system. At some point the siphon starts pulling high enough quantities of particle ice with Fuel such that it migrates toward the engines. Passing into the engines it converts to Steam and causes no particular problem. It may even enhance thrust at some miniscule value. However, it also, as a solid, would "fall out" of suspension and deposit in variable flow areas (due to specific gravity difference) and eventually create flow reduction.

It isn't particularly difficult to imagine this occurring at essentially the same time in both engines, ETOPS isn't foolproof, especially when systems are homogeneous and filled with the (same) Fuel.

I can't imagine what "Unimagined quality" the Fuel possessed to remain so mysterious. Rather than mystifying its audience, perhaps Boeing and FAA should tell the complete tale. A year on with new Physics/Chemistry/Fluidics? Stretches credulity. Just sayin'.

AF

[lomapaseo]

Moving to tongue in cheek mode - Oh to be a fly-on-the-wall in the meeting room where RR are holding their forensic investigations into the decision stage on the FOHE design. Why that design, why not the GE or P&W one? Were the GE and P&W engineers just lucky or did they have knowledge that guided them, and if they did, was this available to RR? I've lots of follow-up questions but will spare you.

There is a lot to be learned about how the industry shares knowledge and, probably more crucially, the authorities must determine how it is that, this most technically advanced global industry, does not know how fuel behaves below -18C.


I think that you need to keep in mind that this is not an engine design problem under regulations Part 33 (engines) but an installation issue under part 25 at the airframers. Considering that the understanding that we have today was not known by the regulators who approved the system, then you can assume that it wasn't recognized as well across multiple manufacturers.

[tanimbar]

Iomapaseo, so my tongue-in-cheek comments were actually foot-in-mouth! Apologies to RR. Thanks for the correction.

Airfoilmod, to tell the complete tale would require an explanation the industry does not yet have and may not have for years as the research is conducted. At least, that is what this ignorant observer considers likely.

To coin a phrase, 'Better to shut up, if you can't put-up'.

Regards, Tanimbar

[airfoilmod]

Not. The shut up part anyway. I don't buy the "unknown behaviour" bit.
You're welcome to it, to each his own. It is typical of the investigative authority to prolong its work; this is not unknown in government. This may raise howls of protest or a delete, but it is my opinion. M.Mouse suggested that there was knowledge of results given to BA and its pilots. That is fine by me. There is however another group with an investment in the "results" that would preclude "secrecy" from being practiced: Other pilots and the travelling public. When all is said and done, I wager the reluctance of the investigation (ers) will not be taken as having been prudent.

AF

[Flight Safety]

AF, I'm willing to accept the explanation that good knowledge of cold fuel behavior is either not well or widely understood.

I think we always learn in aviation, for example take ditching an airliner. We've recently been reminded (again) that it can be done successfully. But how to do it? Probably only a fairly small number of aviators understood it very well prior to the Hudson River accident, while many aviators didn't think it was possible. So that knowledge existed, but wasn't widely known.

I think it may be similar regarding cold fuel behavior.

[airfoilmod]

With respect, I would point out that ditching is a Pilot issue, Cold Fuel chemistry an engineering one. I have the belief that as a group, pilot's have a superior level of Intelligence and practical experience in their field relative to other less demanding pursuits, for very good reason. However, though a pilot may have a fine knowledge of engineering, it isn't a prerequisite for the certificate.

I have a keen interest in Fuel, my life, passengers and freight depend on quality; this quality is expected, and rightly so. I remain surprised at the less than emphatic response to a Chemical, Engineering, Production, and Quality "vacuum of knowledge".

Training and recurrent training emphasize failure, response, innovation, memory, and solution. Well enough two engines fail on a twin, an ETOPS a/c; on top of a rigorous solution and implementation, the consumers of a life dependent product must be patronised with "the great unknown"?

I don't necessarily believe FAA is doing anything unusual here, but when products are found to be life-threatening, generally the appropriate agency appears to act in a more immediate and appropriate time frame.

[Machaca]

I have a keen interest in Fuel, my life, passengers and freight depend on quality; this quality is expected, and rightly so. All hydrocarbon fuel products are produced to a compromised level of specified quality, not ultimate quality. By the time all jet fuel is synthesised by the identical method worldwide we will probably have pumped the earth dry.

I remain surprised at the less than emphatic response to a Chemical, Engineering, Production, and Quality "vacuum of knowledge". I assume you mean among pilots as a group. There is a tremendous amount of knowledge among experts in the various fields that touch on or specialise on fuels.

...consumers of a life dependent product must be patronised with "the great unknown"?Technical and scientific progress hasn't ceased -- far from it. And the discoveries are quite astonishing while at the same time forcing us to lessen our grip on strongly held rules. Physicists can now pause a pulse of light mid-flight!

As previously posited by another poster, it's likely that jet fuel at extreme low temperatures may become a non-newtonian fluid. The time has come for rheologists to study jet fuel at very low temperatures.

Such studies will require not only complex rigs to simulate the requisite conditions, but thousands of evaluations of the myriad possible combinations of jet fuels and additives.

Have a look here for some idea of world jet fuel specs (http://www.exxonmobil.com/AviationGlobal/Files/WorldJetFuelSpecifications2005.pdf) and additives.

[CAPTDOUG]

oeing issues warning to 777 operators

A Delta Airlines 777-200ER was flying from Shanghai, China, to Atlanta last
November when its right engine suddenly lost thrust while the plane was
cruising at 39,000 feet over Montana.

The pilots followed flight manual procedures and descended to 31,000 feet,
where the Rolls-Royce engine recovered and responded normally. The flight,
with 15 crew members and 232 passengers, continued to Atlanta and landed
safely.

That incident would likely not have gotten much attention had the same kind
of Boeing jet, with Rolls-Royce engines, not lost all power in both engines
just before landing at London's Heathrow earlier in the year. The British
Airways 777 crash-landed short of the runway. Several passengers were
injured, but none seriously.

Safety experts eventually decided that the British Airways jet, also on a
flight from China, had flown through unusually cold weather at cruise
altitude and ice apparently formed in part of the engine and blocked the
fuel flow.

On Thursday, Boeing sent a notice to all operators of its 777s with Trent
engines made by Rolls-Royce, advising them that it now believes the Delta
and British Airways incidents appear to have been caused by the same thing –
ice blocking the fuel path.

A Boeing spokesman said Tuesday the "all operators" notice contains a series
of precautionary measures that pilots should take during flight to lessen
the chance ice could cause a sudden loss of engine power.

Eventually, the spokesman said, the FAA can be expected to order a
"permanent fix.'' That would likely mean a redesign of part of the Trent 777
engine.

Boeing would not release a copy of the letter it sent last week. The
spokesman said it is not a public document. But the industry magazine Flight
International obtained a copy and said the Boeing letter describes the Delta
and British Airways incidents as likely being caused by "similar factors.''

More than 700 Boeing 777s, a widebody jet that typically carries from 300 to
360 passengers, depending on the model, are in service with airlines around
the world. About 30 percent have Trent engines.

General Electric and Pratt & Whitney also make engines for the 777, but
those have a different design than the Trent engine from Rolls-Royce and are
not thought to be susceptible to the ice problem. The newest 777s built by
Boeing, the best-selling 777-300ER and the ultra-long-range 777-200LR, are
only powered with GE engines.

In September, the Federal Aviation Administration issued a formal
airworthiness directive that required changes in the way ground crews
prepare 777s with Trent engines and how pilots fly them in extreme cold
weather in response to what investigators found in studying the British
Airways crash in January. Shortly before the FAA issued its warning, Boeing
had sent out an "all operators" notice with a series of recommendations
developed to prevent a similar problem on its 777s with Trent engines.

Boeing recommended, for example, that pilots rev their engines when the fuel
temperature falls to 14 degrees Fahrenheit. That would conceivably dislodge
any ice that might be in the fuel line.

Another procedure recommended by Boeing, and ordered by the FAA, called for
the crew to advance the engine throttles to maximum thrust for 10 seconds
before descending on flights that have maintained the same altitude for at
least three hours, if the fuel temperature is below 14 degrees.

Those procedures have been revised in the Boeing bulletin sent last week,
following the Delta incident.

Boeing now recommends that pilots advance engine throttles to maximum thrust
before descending on flights that have maintained the same altitude for two
hours, not three.

Also in its latest notice, Boeing recommends that pilots, during the descent
for landing, reduce engine power to full idle for at least 30 seconds. By
reducing fuel flow, engine oil heat can melt any ice that may have
accumulated.

The FAA, as it did in September, is likely to make Boeing's latest
recommendations mandatory.

The 777 has never had a fatal crash since it entered service with United
Airlines in 1995. But the Delta and British Airways incidents have given
safety experts cause for concern, in large part because they are apparently
dealing with a previously unknown phenomenon.

The British Airways crash occurred Jan. 17, 2008, as the 777-200ER, with 152
passengers and crew members, approached Heathrow after a flight from
Beijing. Both engines failed to respond to autopilot commands for thrust as
the plane approached the airport.

It turned into one of the most puzzling aviation accidents in modern times.
The plane was badly damaged but was mostly intact, so investigators had all
the physical evidence in hand to look for clues. But one thing was missing –
the ice. The key piece of evidence had literally melted away.

Investigators now believe the problem is with the fuel-oil heat exchanger
system on the Trent 777 engine.

Boeing engineers, according to Flight International, have determined by
working in the laboratory that the heat generated by the Rolls-Royce
fuel-oil heat exchanger is not adequate to prevent moisture in the fuel from
freezing. When that happens, ice can form that blocks fuel to the exchanger,
"starving the engines,'' according to the magazine.

The General Electric and Pratt engines on the 777 have a different fuel
system architecture.

"Based on our knowledge of the system configurations, scenario studies and
laboratory test results, we do not believe that immediate action is
necessary or warranted for 777s powered by other engine types or non-777
airframes regardless of engine type,'' the Boeing letter sent to 777
operators last week states, according to Flight International.

[airfoilmod]

So the cold fuel transits the system, waits with liquid water in its composition so that it can freeze after entering the pylon and the enhanced heat of the HE? I think that isn't likely. Again, at the temps in the tanks, there would be no liquid water in the fuel. Something Capt. Cargill suggested covers more ground; an upstream "snowstorm" that caused cavitation at the engines. The "snow" (small granular water ice) would have formed as early as in the trucks (A/P tankage) prior to uplift.

Another problem with the Boeing memo as supplied. The assumption is the cavitation was caused by ice blocking proper flow to the HP pumps, if the blockage occurred at the HE does Boeing suggest the Fuel was flowing fine until the ice formed at the exchanger? I suppose the tests are ongoing relative to the FOHE and Boeings fully mocked up system. From the initial response of both engines one could assume that the exchangers were collecting a suspended (preformed) "precipitate" or subjected to the necking down of the exit aperture as ice quickly formed ahead of the exit.

It would be folly for Boeing to target only the RR if it suspected at all that the other engine types were in the least susceptible to the anomaly.
It would be likewise almost unthinkable for Boeing to allow a vulnerability to problems with the fuel to go unreported. This would appear to exonerate the fuel by default, the GE and Pratts as well. Let's not forget that rollbacks occurred well into the long flight, lending some suspicion to a greater concentration of particle ice with time aloft. Also, that on Delta, the rollback appears to have occurred without a demand for increased thrust, as on 038.

AF

[Smilin_Ed]

Also, that on Delta, the rollback appears to have occurred without a demand for increased thrust, as on 038.

Which came first on 038, the rollback or the demand for thrust? :hmm:

[CONF iture]

Which came first on 038, the rollback or the demand for thrust?
Published data seem to indicate both 038 rollbacks came as thrust was already increasing ... but ?

Another question is : Did the Delta fuel pump show signs of cavitation afterward ?

[VFD]

From the Flight Global article, it appears the GE and PW design recirculates some of the heated fuel back to the upstream face of the FOHE, thus preheating the new cold fuel approaching the upstream FOHE face (thus melting any water ice before reaching the FOHE). The Trent FOHE does not appear to have this warmed fuel recirculation feature, thus the fuel reaching the upstream face of the FOHE is colder than on the GE or PW designs

It appears at least AAIB is onto something here and has done extensive testing to identify the problem with the water ice ahead of the FOHE. So now the solution will have to be some sort of a redesign by RR and of course tested and accepted by the correct authorities.

The question goes back to did GE and PW have previous knowledge of problems with ice, just returned the warmer fuel due to convenience of a place to return the fuel, or dumb luck?

Then again I would also wonder if other RR engines are plumbed in the exact manner of engines in question on the T7 and just not exposed to the long periods cold soaked conditions connected to the T7.

VFD

[Pinkman]

So the cold fuel transits the system, waits with liquid water in its composition so that it can freeze after entering the pylon and the enhanced heat of the HE? I think that isn't likely. Again, at the temps in the tanks, there would be no liquid water in the fuel. Something Capt. Cargill suggested covers more ground; an upstream "snowstorm" that caused cavitation at the engines. The "snow" (small granular water ice) would have formed as early as in the trucks (A/P tankage) prior to uplift.

There are so many errors in what you have written that you clearly havent a clue either about phase-separation chemistry, airport bulk storage or apron hot-hydrant / hydrant servicer systems. If you dont KNOW why dont you just say nothing?

[phil gollin]

I am still extremely disturbed that people are taking the (relatively unofficial) Boeing statement too seriously.

Any proper solution would need to explain the problem scientifically and (eventually) come up with a new set of rules both for Fuel Specification(s), for pipework/accessories installations and flight planning and operations.

THEN ALL aircraft, no matter what engine, would need to be checked against the new rules.

---------------

Two other things ;

(i) Still three cheers for any useful information.

(ii) Any real explanations for the BA flight having suffered a dual failure so almost simultaneously ?


------------------

Grasping at partial straws is not a solution.

.

[M.Mouse]

If you dont KNOW why dont you just say nothing?

Because that is not his modus operandi!

[lomapaseo]

Any proper solution would need to explain the problem scientifically and (eventually) come up with a new set of rules both for Fuel Specification(s), for pipework/accessories installations and flight planning and operations.

THEN ALL aircraft, no matter what engine, would need to be checked against the new rules.


Absolutely agree:ok:

We need to learn and avoid pointing fingers at persons/organizations and stop throwing stones inside a glass house that we are all inside.

Since it's obvious to me that the industry (regulators, engine and airframers )did not know of this combination beforehand it just happend to be a RR installation that first illustrated the weakeness in all our collected ignorance.

[phil gollin]

Quote :-

......... Since it's obvious to me that the industry (regulators, engine and airframers )did not know of this combination beforehand it just happend to be a RR installation that first illustrated the weakeness in all our collected ignorance.

unquote


I knew someone intimately involved in the Kings Cross fire. There, both before during and after the official enquiry there were masses of misinformed criticism. Most people nowadays will say it was simplistically the combination of wooden treads and build-up of rubbish in the under-escalator area (plus poor emergency procedures).

Actually the main reason was the flash-over effect caused by the layout of the tunnels - something never expected and indeed "new" in terms of underground railway operation. The experts know what happened, the general public just have a simplistic view.

(The final costs of all the remedial works has been vast - and is only now being completed - I have a vague feeling the same might be a case here).

.

[phil gollin]

Actually there seems just as few facts in that piece as any other.

Still no information on where the "water" for the ice came from.

Still no information on the process whereby the ice formed and acted so regularly on two separate systems

Still no scientific/engineering explanations and new rules to cover ALL aircraft and ALL engine installations.

--------------------------------------

I have copied the piece below ;


Boeing issues warning to 777 operators

Below is a story I just filed, following up on the British Airways crash at Heathrow a year ago.

BY James Wallace
P-I aerospace reporter

A Delta Airlines 777-200ER was flying from Shanghai, China, to Atlanta last November when its right engine suddenly lost thrust while the plane was cruising at 39,000 feet over Montana.

The pilots followed flight manual procedures and descended to 31,000 feet, where the Rolls-Royce engine recovered and responded normally. The flight, with 15 crew members and 232 passengers, continued to Atlanta and landed safely.

That incident would likely not have gotten much attention had the same kind of Boeing jet, with Rolls-Royce engines, not lost all power in both engines just before landing at London's Heathrow earlier in the year. The British Airways 777 crash-landed short of the runway. Several passengers were injured, but none seriously.

Safety experts eventually decided that the British Airways jet, also on a flight from China, had flown through unusually cold weather at cruise altitude and ice apparently formed in part of the engine and blocked the fuel flow.

On Thursday, Boeing sent a notice to all operators of its 777s with Trent engines made by Rolls-Royce, advising them that it now believes the Delta and British Airways incidents appear to have been caused by the same thing – ice blocking the fuel path.

A Boeing spokesman said Tuesday the "all operators" notice contains a series of precautionary measures that pilots should take during flight to lessen the chance ice could cause a sudden loss of engine power.
Eventually, the spokesman said, the FAA can be expected to order a "permanent fix.'' That would likely mean a redesign of part of the Trent 777 engine.

Boeing would not release a copy of the letter it sent last week. The spokesman said it is not a public document. But the industry magazine Flight International obtained a copy and said the Boeing letter describes the Delta and British Airways incidents as likely being caused by "similar factors.''

More than 700 Boeing 777s, a widebody jet that typically carries from 300 to 360 passengers, depending on the model, are in service with airlines around the world. About 30 percent have Trent engines.

General Electric and Pratt & Whitney also make engines for the 777, but those have a different design than the Trent engine from Rolls-Royce and are not thought to be susceptible to the ice problem. The newest 777s built by Boeing, the best-selling 777-300ER and the ultra-long-range 777-200LR, are only powered with GE engines.

In September, the Federal Aviation Administration issued a formal airworthiness directive that required changes in the way ground crews prepare 777s with Trent engines and how pilots fly them in extreme cold weather in response to what investigators found in studying the British Airways crash in January. Shortly before the FAA issued its warning, Boeing had sent out an "all operators" notice with a series of recommendations developed to prevent a similar problem on its 777s with Trent engines.

Boeing recommended, for example, that pilots rev their engines when the fuel temperature falls to 14 degrees Fahrenheit. That would conceivably dislodge any ice that might be in the fuel line.

Another procedure recommended by Boeing, and ordered by the FAA, called for the crew to advance the engine throttles to maximum thrust for 10 seconds before descending on flights that have maintained the same altitude for at least three hours, if the fuel temperature is below 14 degrees.

Those procedures have been revised in the Boeing bulletin sent last week, following the Delta incident.

Boeing now recommends that pilots advance engine throttles to maximum thrust before descending on flights that have maintained the same altitude for two hours, not three.

Also in its latest notice, Boeing recommends that pilots, during the descent for landing, reduce engine power to full idle for at least 30 seconds. By reducing fuel flow, engine oil heat can melt any ice that may have accumulated.

The FAA, as it did in September, is likely to make Boeing's latest recommendations mandatory.

The 777 has never had a fatal crash since it entered service with United Airlines in 1995. But the Delta and British Airways incidents have given safety experts cause for concern, in large part because they are apparently dealing with a previously unknown phenomenon.

The British Airways crash occurred Jan. 17, 2008, as the 777-200ER, with 152 passengers and crew members, approached Heathrow after a flight from Beijing. Both engines failed to respond to autopilot commands for thrust as the plane approached the airport.

It turned into one of the most puzzling aviation accidents in modern times. The plane was badly damaged but was mostly intact, so investigators had all the physical evidence in hand to look for clues. But one thing was missing – the ice. The key piece of evidence had literally melted away.

Investigators now believe the problem is with the fuel-oil heat exchanger system on the Trent 777 engine.

Boeing engineers, according to Flight International, have determined by working in the laboratory that the heat generated by the Rolls-Royce fuel-oil heat exchanger is not adequate to prevent moisture in the fuel from freezing. When that happens, ice can form that blocks fuel to the exchanger, "starving the engines,'' according to the magazine.

The General Electric and Pratt engines on the 777 have a different fuel system architecture.

"Based on our knowledge of the system configurations, scenario studies and laboratory test results, we do not believe that immediate action is necessary or warranted for 777s powered by other engine types or non-777 airframes regardless of engine type,'' the Boeing letter sent to 777 operators last week states, according to Flight International.



============================================

[Torquelink]

Extract from Boeing MOM issued Thursday 26th Feb:

Rolls-Royce has developed a modification to the FOHE to mitigate the potential for a future fuel system ice accumulation and release event resulting in a restriction at the inlet to the FOHE. Information on the proposed modification is provided via the ref /E/ Rolls-Royce Worldwide Communication (WWC). As noted in ref /E/, the modified FOHE is similar to the existing unit except that the fuel tube inlets are flush mounted to the inlet face plate instead of being proud of the inlet face plate. Testing has demonstrated a significant improvement in the tolerance to the arrival of ice at the inlet face plate in respect of ice quantity and fuel temperature.

Boeing and Rolls-Royce are working with the FAA and EASA to determine the most expedient path to certify the proposed FOHE redesign. Pending certification of the redesigned FOHE, Rolls-Royce is targeting service bulletin release in the third quarter of 2009. Per the ref /E/ WWC, the plan for allocating modified FOHEs is currently being developed and will be communicated with each operator individually once available.

[phil gollin]

Fascinating -- but it doesn't actually address the process that MIGHT have caused the crash, or where the water came from.

Nor is it a set of rules that applies to ALL aircraft with all types of engine.

Keep these announcements in context.

.

[airfoilmod]

My 2 cents, as a non engineer type, still relates to fuel and extended periods of very cold and very stable cruise. Both incidents occurred after very long periods of cold soaked and static cruising. All fuel has water in it, the spec allows small amounts. If the a/c tanks fuel prior to launch, it may already contain minute crystalline frozen water, albeit in trace amounts. Dispersed throughout the a/c tanks in some homogeneous mixture, it can certainly collect in small or "restrictive passages" (FOHE).
Built up as a "powdery" rather than a "solid" mass, it may collect in such a manner over time, that it allows cruise thrust, the flow of fuel acting to prevent continued necking down of the constricted passages so affected.
Without being specific due to my limited expertise, I can envision this "snowy" mass preventing higher thrust levels, or, due to additional accretion, maintaining current thrust, causing unresponsive power.

In the case of BA038, sudden full demand may have redistributed this occlusive mass downstream, packed it up and caused cavitation.

For Delta, the plug may simply have shifted on its own.

Anticipating the hue and cry from true believers in ETOPS, it isn't hard to imagine roughly simultaneous faults, given that at periods of long cruise, the systems acclimate and perform as one, essentially, given that there is no discrepancy in design, one from the other. Modern machining, chemistry and refining contributes to non anomalous behaviour of systems.

Then again, the Trent FOHE may melt and allow the ice to refreeze downstream. Over time, (long cruise) this could compromise fuel flow in the traditional way.

[Smilin_Ed]

Were the Fuel Oil Heat Exchangers for either GE or RR engines specifically designed to warm the fuel as well as cool the oil or was increasing fuel temperature simply a fortuitous byproduct? (Actually, increased fuel temperature would incrementally improve thermal efficiency.)

[lomapaseo]

(Actually, increased fuel temperature would incrementally improve thermal efficiency.)

How so, got any numbers?

[phil gollin]

Airfoilmod,

Please don't get me wrong, I like more information. All I worry about is that people MAY be being misled by short-term ideas or solutions. What is needed is a full scientific answer with a proper engineering solution which applies to all aircraft and engine installations.

It may (!) be that only one aircraft/engine installation combination is found to be at risk, but that is so unlikely as to be ridiculous. I just want people looking at the "big picture", not just concentrate on little ones.

.

[fcom]

I regularly operate on the China to Heathrow route and in winter the fuel temp always goes to around -42c sometimes -49c after around 6 hrs of flight.The minimum temp the fuel can drop to is -40c if USA fuel used and -49c for other countries. The engines can be at flight idle for around 20 mins during the descent with temps a lot lower than the fuel would have been on short finals which would have been around -8c or even warmer.
I'm pretty sure if there was any ice present it would have accumalated long before then and most certainly flagged up in the descent.

[Oluf Husted]

Dear fcom,

I have earlier, 2/3, 8/4, 1-5/5 and 3-4/7 (July) 2008, been writing, on this thread, about my theory, that core-icing, due to an ineffective or "turned off" engine anti-ice system, had the engines hesitate, and after "landing" just melt away.

This can also have been the cause in Amsterdam (TK1951)

So have a look, and let me know, if you have had the same thoughts.

Oluf Husted www.whistleblowers.dk

[answer=42]

Might this thread (http://www.pprune.org/engineers-technicians/335233-water-checks-procedures.html), especially the discussion of water from condensation, be relevant to the discussion?

[DC-ATE]

Has a "final" report come out yet on this accident?

[lomapaseo]

So have a look, and let me know, if you have had the same thoughts

is this for voting or only for expert opinions:confused:

At any rate the answer is No

apparently you don't understand anti-icing systems nor core icing.

However having formed an opinion and your own web site I doubt that you will change your mind seeking only support for your theory.

[airfoilmod]

On board with that. My feeling all along is that information is being grasped a little too tightly by AAIB. FAA and NTSB operate a little differently. I do not buy the "Unknown characteristics". I think it is a wheeze. As time marches on, the leakage from the authority (not AAIB) has firmed up what Cargill and others were saying from the very beginning.

So it's the Trent? Boeing says so. Commercialism and turf battles have no place vis a vis safety issues. If that's what's happening.

[FrequentSLF]

At any rate the answer is No

apparently you don't understand anti-icing systems nor core icing.

However having formed an opinion and your own web site I doubt that you will change your mind seeking only support for your theory.

As a reader of this forum I found, with all the due respect, your post absolutely meaningless. If you do not agree with a theory you should explain the reasons why you do not agree.

[Carnage Matey!]

From that website:

The air is routed to the fan-cone or spinner via metal tubing, hollow static stator- and inlet guide-vanes in order to keep the temperature on the most ice-prone parts above freezing temperature. When being sucked into the engine again, the air also keeps the back side of the big front fan-blades free of ice.

Not on any high-bypass jet engine I've ever operated. Engine anti ice keeps the nacelles ice free but it certainly doesn't route air to to spinner or fan cone nor does it prevent fan blade icing. I suspect this may be but one of many inaccuracies on that site.

Edited to add I've just spotted a complete lack of understanding of the BA LAX-LHR 3 eng flight in there too.

[Rightbase]

The thread you quote says the amount of water that can accumulate is quite substantial.

Against - there was a limited time window for it to accumulate after the inspection.
For - water scavenge is of doubtful effectiveness below freezing.

Any accumulated 'water' could all appear at once as the empty centre tank thawed out during the descent, and be scavenged through the still frozen main tanks to be fed to the two 'independent' engine systems as ice 'droplets'.

[vapilot2004]

Chicken Or Egg?
Were the Fuel Oil Heat Exchangers for either GE or RR engines specifically designed to warm the fuel as well as cool the oil or was increasing fuel temperature simply a fortuitous byproduct? (Actually, increased fuel temperature would incrementally improve thermal efficiency.)

Oil cooling is a requirement, but the heat exchangers main purpose is to warm the fuel.

[vapilot2004]

So it's the Trent? Boeing says so. Commercialism and turf battles have no place vis a vis safety issues. If that's what's happening.

Boeing hasn't said exactly that. It is the combination of the Trent engine and the airframe fuel system that will require tweaking. Engineering on both sides obviously missed some low-temperature and possibly fuel quality management gotchas.

[CV880]

40 odd years ago I worked for a DC8-50 operator that experienced ice blockage of the inlet to the Fuel Oil Heat Exchangers on engines 1 and 4 on one particular sector. I don't recall if there were any power reductions as a result but the indicated fuel pressure on 1 and 4 used to drop late in the 9.5 hr flight. Investigation revealed impact icing on the fuel inlet end of the heat exchanger core. Part of the problem was the fuel loaded at HNL contained too much water as the tank farm capacity back then did not allow sufficient settling time before use. Engines 1 and 4 only were affected because the coldest fuel was in tanks 1 and 4 toward the end of the sector.
The fix was to reverse the oil flow through the FOHE. The original design had the hot oil entering at the fuel exit end and the cooled oil exiting at the fuel inlet which I recall was supposed to be the more thermally efficient flow but by reversing the flow the hot oil went into the fuel inlet end of the core and stopped the ice from building up on the FOHE core.

[sky9]

CV880

That should sort the problem out for little more than a couple of dollars:)

[Von Klinkerhoffen]

Dear fcom,

I have earlier, 2/3, 8/4, 1-5/5 and 3-4/7 (July) 2008, been writing, on this thread, about my theory, that core-icing, due to an ineffective or "turned off" engine anti-ice system, had the engines hesitate, and after "landing" just melt away.

This can also have been the cause in Amsterdam (TK1951)

So have a look, and let me know, if you have had the same thoughts.

Oluf Husted www.whistleblowers.dk (http://www.whistleblowers.dk/)


I have to agree with lomapaseo , you are confusing nacelle icing with engine core icing , two completely different things . As for your website , at least try to get your facts right before trying to impress a group of professionals on a forum !!

Besides , how on earth does engine core icing explain the HP fuel pump cavitation exhibited by both engines ??

[lomapaseo]

Vapilot2004

It is the combination of the Trent engine and the airframe fuel system that will require tweaking. Engineering on both sides obviously missed some low-temperature and possibly fuel quality management gotchas.

Agree

No doubt all the manufacturers and regulatory agencies are reviewing their specific systems.

I doubt that there will be a regulatory wording change but a "special condition" might be applied to new installations.

[airfoilmod]

There seems to be some parsing going on. No axe here, the Fuel/Powerplant interface certainly must be rigorously examined. Boeing built a freestanding Tank/Supply mock-up/test-bed, and then concluded that the Trent has issues. Can the Plumbing be re-designed to accomodate the Trent's shortcomings? Add fine screen filters and robust bypass systems, and fuel pre-heat? For good measure refit PW and GE equipped frames so the Trent doesn't feel picked on? I may be missing something, it wouldn't be the first time or the last; Isolating the architecture of the RR F/OHE for criticism appears to be Boeing's conclusion.

AF

[sooty655]

vapilot2004
Oil cooling is a requirement, but the heat exchangers main purpose is to warm the fuel.


I don't think so. The system controls only on the oil temperature. When the oil doesn't need cooling, there is no oil flow through the exchanger, and no fuel heating. The (very small) efficiency gain when the fuel is being (slightly) heated is a bonus, not a design consideration.

Sooty

[Smilin_Ed]

Quote:
(Actually, increased fuel temperature would incrementally improve thermal efficiency.)
How so, got any numbers?

No. Remember, I said incrementally. I doubt if it would even be measurable. But, any heat that you recover from the oil and feed back into the fuel means more heat to be released when the fuel burns. Just basic thermodynamics.

[phil gollin]

Yet again.

People seem to be reading too much into Boeing's leaks/announcements.

a: They still doesn't explain where the water came from.

b: They don't SEEM to explain the almost simultaneous and near-enough exactly similar problem in two separate systems

c: There is no scientific explanation

d: There are no proposed new rules for fuel and/or engine installations which shall apply to ALL aircraft.


Keep things in perspective.

.

[Swedish Steve]

I don't think so. The system controls only on the oil temperature. When the oil doesn't need cooling, there is no oil flow through the exchanger, and no fuel heating

On the Trent the FOHE is always on. There are no controls at all on the fuel flow side, and there is only a bypass on the oil flow side to enable to oil to bypass at very low temp (when the oil is below zero when starting)
The oil temp control system controls the AOHE which is normally closed, and opens at high oil temps to pass fan air through a heat exchanger to cool the oil.

[Machaca]

Phil:

a: They still doesn't explain where the water came from.Same as always. Nothing new to explain.

b: They don't SEEM to explain the almost simultaneous and near-enough exactly similar problem in two separate systemsNear-enough identical separate systems in same environment produced almost simultaneous results. What more is there to explain?

c: There is no scientific explanationWhen it is fully sussed out it will appear in the appropriate peer-reviewed journals.

d: There are no proposed new rules for fuel and/or engine installations which shall apply to ALL aircraft.Sweeping changes require specific knowledge - see item C above. In the meanwhile, making changes to anything other than the affected airframe/powerplant will not improve safety by a warrantable amount.

[phil gollin]

So Machaca, you are willing to go off thinking there is a solution to an unknown problem (where did the water come from), with an unknown process (the near-enough simultaneous timing and effect on two separate systems) without any scientific explanation or idea how many other aircrat instalations are involved.

You've just demonstrated that however worthy any small action is, it is not a proper solution, merely a palative.

.

[sooty655]

On the Trent the FOHE is always on. There are no controls at all on the fuel flow side, and there is only a bypass on the oil flow side to enable to oil to bypass at very low temp (when the oil is below zero when starting)
The oil temp control system controls the AOHE which is normally closed, and opens at high oil temps to pass fan air through a heat exchanger to cool the oil.


Afaik the bypass on the oil side is thermostatic, and diverts oil flow through or around the FOHE to maintain oil temperature. It is designed to cope with a wide range of fuel temperatures from freshly loaded ambient to altitude-soaked cold. With very cold fuel, most oil will bypass the cooler with only a bare minimum passing through to maintain oil temperature. The heating effect on the fuel will be minimal.

Sooty

[Rightbase]

Why all the emphasis on
unknown problem (where did the water come from) ?
With respect, we knows where the water in fuel tanks (ground based or airborne) comes from - it comes from the atmosphere - either warm wet air being cooled, or suspended moisture AKA cloud.
Descending through cloud with a large empty centre tank for instance will introduce water in some form. If the tank is cold, the moisture will condense as frost all over the inner surface.
The question is not where does the water (or ice) come from, but how and where does so much manage to successfully accumulate, and yet be suddenly released in such volume that it can bring an aircraft down?
The sudden release looks like melting. The ability to bring the aircraft down looks like refreezing. The path from warm(?) centre tank to engine passes through the (cold?) main tanks.
Other possibilities may exist - that is simply one obvious sequence along the fuel path.
The question is which possibility actually became a reality?

[UNAQAS]

Anyone got any information on number (if any) of following aircraft that had to execute missed approach immediately after the accident? Have been following the thread since early on and don't recollect if it ever was mentioned.

[HeathrowAirport]

I think a few went around, about 2-4, and a few sidestepped onto 27R.

I think it was 2 sidesteps and 2 go arounds, but not sure. Someone from EGLL Tower shall be able to give the exact.

[UNAQAS]

Thank you Heathrow' for your quick response, just wondering if aircraft was being vectored in the middle of usual heavy traffic (as we all assume) or if perhaps had a pseudo-CDA of sorts from LAM @ FL90 on the day.....Not much info in the interim report regarding time/length of transition onto final and the ILS. You'd expect fuel flows to have been higher than those recorded with aircraft clean in the hold @ 90, if level flight ensued at some point with flap extended later on at lower altitudes.

By the way, I'm not reading too much into this, like all drivers who've been around the block, am having a hard time accepting some of the theories being put forward as intuitively, they go against the grain a bit.

[Swedish Steve]

Afaik the bypass on the oil side is thermostatic, and diverts oil flow through or around the FOHE to maintain oil temperature. It is designed to cope with a wide range of fuel temperatures from freshly loaded ambient to altitude-soaked cold. With very cold fuel, most oil will bypass the cooler with only a bare minimum passing through to maintain oil temperature. The heating effect on the fuel will be minimal.

Sooty

Sorry sooty but the AMM doesn't agree with you
AMM 79-20
* Oil pressure relief bypass valve
If the engine oil is too cold or the heat exchanger oil core is
clogged, the pressure relief bypass valve opens.

The fuel temp does not affect the operation at all. Only oil temp. And by too cold RR mean around zero deg C.

[Shaka Zulu]

Swedish Steve you are right.

Btw
For Trent 895's the restriction for Take Off is that the OIL temp has to be above 50Deg Centigrade ai out of the amber band.
This is not the case on GE90's.
I still dont know why there is this distinction

[DC-ATE]

A few days ago I asked if the "final" report was out yet on this accident. I have not seen any reply. So.....I am wondering why a malfunctioning FADEC seemingly has been ruled out. I only see discussion on water in the fuel.

[lomapaseo]

I am wondering why a malfunctioning FADEC seemingly has been ruled out. I only see discussion on water in the fuel.

Ruled out by whom:confused:

The AAIB who hasn't published their final report detailing all considerations? or by Pprune who have discussed it to death?

I really am in favor of having a quiz scattered within these Pprune threads. If you flunk the quiz on discussion subjects than you shall be banned from posting for one week in the thread.

[airfoilmod]

Rumours and News is just that. If it was worthy of quizzes and credential checks, it would cost money. One gets what one pays for, silk purse, sow's ear, etc. I don't want to redo groundschool.

[sooty655]

The fuel temp does not affect the operation at all. Only oil temp. And by too cold RR mean around zero deg C.


I think we are saying the same thing with different words. I agree the fuel temperature has no direct effect on the bypass. However, the continuous flow of cold fuel would grossly overcool the oil unless the bypass diverted oil around the FOHE to maintain the bulk oil temperature.

All the fuel flow always goes through the FOHE, but at low fuel temperatures, most of the oil goes around the FOHE via the bypass.

Sooty

[judge.oversteer]

I'm with you on this.

Although I think the money is on the "ice bullets' theory.

JO

[airfoilmod]

If, unlike the GE and PW designs, RR had designed a system with HE bypass for Fuel, based on Pressure, this thread would not have appeared.
A packed up FOHE fuel side, causing cavitation and no flow, would have been bypassed by a simple gate valve in front and behind the Plug.
Electrically (solenoid) operated slaved to a pressure sensor.

AF

[phil gollin]

Airfoilmod,

Where do you get your scientific information ?

There seems not to have been enough ice to cause the icing - unless you know better (if so please state how you obtained it).

There is no report stating what is formally believed to have happened (again unless you know something that you are not saying).

And, unless this accident is properly explained a similar one affecting a totally different aircraft/engine configeration might occur.

You seem to be taking too much credence in partial information.

.

[Swedish Steve]

However, the continuous flow of cold fuel would grossly overcool the oil unless the bypass diverted oil around the FOHE to maintain the bulk oil temperature.

All the fuel flow always goes through the FOHE, but at low fuel temperatures, most of the oil goes around the FOHE via the bypass.

Sooty, I see you have worked for RR so I must bow to your knowledge. I only know what I was taught on the AMEL course, and read in the AMM (which is a bit basic on the B777)

The last iteration of RB211 the -524G/H on the B744 and B763 had a very complicated system on two FCOCs with bypass valves for low fuel temp and high fuel temp. But these only controlled the flow of oil, not the flow of fuel.

But engines transfer large quantities of heat to the oil, which is passed to the fuel.
The Trent 800 also has an AOHE, air cooled oil cooler. This is controlled by the FADEC to cool the oil when the FOHE can't cope. If the AOHE control system fails, the valve is driven full open. It is covered in the MEL and can be locked part open. There is a caution in the MM
"Make sure you lock the AOHE in the open position. If the AOHE is not locked correctly, oil and fuel temp can rise much higher than normal and cause damage to the engine"

Do you have any reference to how the FOHE Oil bypass valve works? The AMM just says low temp.
The operating oil temps are 50-185 degC, and norm about 100-120. What is low?

[Machaca]

Phil:

There seems not to have been enough ice to cause the icing
For each side, something on the order of 20,000 gallons of jet fuel with an enormous number of tiny suspended ice particles transited through the fuel system for upwards of ten hours. The accretion of ice is to be expected.


And, unless this accident is properly explained a similar one affecting a totally different aircraft/engine configeration might occur.It is perhaps likely that thousands of flights in similar profiles over the years have been close to succumbing to ice accretion induced trouble, only to have landed in time.

Some by minutes, others by hours. That doesn't change the phenomenal statistical success achieved to date.

You may feel better if you join a rheology forum and a fluid dynamics forum and demand their immediate combined action on sub-zero kerosene ice and its accretion properties in tubular delivery systems.

[precept]

Following is a link to the latest AD note regarding the roll back incident.

Justia Regulation Tracker Airworthiness Directives: Boeing Model 777?200 and ?300 Series Airplanes Equipped with Rolls-Royce Model RB211?TRENT 800 Series Engines , - Federal Aviation Administration - 9565?9568 [E9?4650] (http://regulations.justia.com/view/137011/)

Below is an alternate link if Justia link is not available:

FR Doc E9-4650 (http://edocket.access.gpo.gov/2009/E9-4650.htm)


Partial content of AD:


Since we issued AD 2008-19-04, we received a report of a single-
engine rollback as a result of ice blocking the fuel oil heat exchanger
(FOHE) on a Model 777 airplane equipped with Rolls-Royce Model RB211-
TRENT 800 series engines. The data confirm that ice accumulates in the
fuel feed system and releases after a high thrust command, creating
blockage at the FOHE and resulting in the inability of the engine to
achieve the commanded thrust. Examination of the data from the rollback
shows that the second of two maximum thrust step climbs was performed
approximately 40 minutes prior to the thrust rollback. Ice was released
within the fuel system during the step climbs and formed a restriction
at the FOHE of the affected engine, as evidenced by an increase in
engine oil temperature. Further analysis of the data shows that ice
accretes in the fuel system more rapidly and at warmer fuel
temperatures than previously indicated, and ice may build up gradually
on the FOHE before causing the engine to rollback. The data from this
event, in combination with Boeing fuel lab testing, demonstrates that
reducing the fuel flow to minimum idle levels will clear any ice
accumulation at the FOHE within a few seconds.
All of the testing and research has been conducted on Boeing Model
777-200 and -300 series airplanes, equipped with Rolls-Royce Model
RB211-TRENT 800 series engines. Initial review of other Model 777
airplane engine combinations has not revealed the same vulnerability to
the identified unsafe condition.

[HarryMann]

What is low?

< 50C

e.g. 40C

[vapilot2004]

If, unlike the GE and PW designs, RR had designed a system with HE bypass for Fuel, based on Pressure, this thread would not have appeared.
A packed up FOHE fuel side, causing cavitation and no flow, would have been bypassed by a simple gate valve in front and behind the Plug.
Electrically (solenoid) operated slaved to a pressure sensor.

AF

Trouble with this idea is the ice would muck up the works downstream. Pressure regulators and flow metering devices have much smaller passages than the FOHE's.

[airfoilmod]

Actually not. To gain surface area for rapid transfer, the HE has numerous "tubes" of small diameter to hasten thermal gain. There is a picture of one on thread, by Machaca. (my impression of said pic, af)

I say "Gate Valve" for a reason, they are as large or larger than the Fuel line itself, and for the reasons you state.

AF

[vapilot2004]

Interesting. So you're saying the combined cross-sectional area of the FOHE's is actually smaller than a metering valve or nozzle? Or are you referring to only one of many tubes within the exchangers?

I had always envisioned a fin-on-tube arrangement for these FOHE's. Perhaps this type is only for the air cooled variety.

[sooty655]

Swedish Steve
Do you have any reference to how the FOHE Oil bypass valve works? The AMM just says low temp.
The operating oil temps are 50-185 degC, and norm about 100-120. What is low?


The bypass valve is opened by differential pressure, basically similar to a relief valve. You were right that there is no thermostatic bypass, only the diff pressure one.

I haven't been able to find out the oil temperature at which the differential pressure would open the valve, but I agree with HarryMan it is likely to be around the bottom of the normal operating range.


vapilot2004
I had always envisioned a fin-on-tube arrangement for these FOHE's.


No finned tubes in the FOHE. It has a bundle of straight through small bore tubes for the fuel to flow through. The oil passes through a jacket around the tubes, with baffle plates to cause a zig-zag flow to maximise contact with the outside of the tubes.

As you said, finned tubes are normally used on air cooled arrangements, to maximise contact area for the air.

Sooty

[airfoilmod]

"Restriction" rapidly diminishes the "area available for transit". One large pipe is best if what you want is Flow, related to viscosity and demand, etc. It really isn't critical the cross-section, but the available gross area.
Several small pipes can perform as well as one big one. Introducing another variable, Ice, changes everything. The small openings pack first, but may remain open if demand is, say, Idle or flight idle. Increasing demand may be the same as further restricting the cross section with constant flow. I don't have any more information than anyone else, and quite possibly less than some, but the bypass, while preventing a case that Boeing proposes, eliminates heat exchange. The GE has a recirc feature that may make the ice more susceptible to transit, eg forestalling refreeze.

If the Fuel is VERY cold, it may cool the Oil too much, also a bad thing.
While it's interesting to discuss these problems, my basic concern is the same as Phil Gollins. I'm a convert to ETOPS and have high expectations, I'm no engineer, but I dislike the lack of information forthcoming from the authority. So far, I like Boeing's approach better than the other's.

[M.Mouse]

.....but I dislike the lack of information forthcoming from the authority. So far, I like Boeing's approach better than the other's.

You think that the AAIB and Boeing are acting individually without sharing of information and in full knowledge of each other's actions?

The information which is known and is necessary to be promulgated to reduce the risk of the events recurring is being promulgated.

What exactly is your beef except you think every move by the AAIB should be publicised and dissected before a definitive, accurate and full report is ready? Perhaps it is all a big conspiracy.

[airfoilmod]

I suppose you hadn't heard of the second rollback. If everything you say is true, evidently enough information was not forthcoming; perhaps Delta wasn't informed. The thing you have with conspiracies is a little over the top. I take note that you are annoyed at my irritation.

Let me be blunt. If BA038 had started descent a bit sooner, and was the least little bit lower than they were, it would have been disastrous. If Delta couldn't relight, and lost a second engine, Have you ever flown over the Rocky Mountains?

AF

[Bis47]

My memory can fail ...

Did I really read that the Delta Airplane that recently experienced a roll back over the Rockies also was originated from China?

If true ... that is too much of a coïncidence.

[jfill]

It was Delta Flight 18, from Shanghai to Atlanta. Happened at 39,000ft. The crew descended to 31,000ft and restarted. Continued on to KATL

[Flight_Idle]

FOHE, I find it suprising that the fuel is directed to flow through the narrow bore pipes & oil throught the larger bore outer casing. Why not have it the other way round? the heat exchange would surely be the same?

There still seems to be some confusion over how the correct oil temperatue is maintained. Does the oil flow switch on & off to give the desired result? if so, this could effect ice melting, which has been said to take only a few seconds when engine power is demanded? (That was said on one report, but clearly did not happen when engine power was demanded on the incident in question)

[Smilin_Ed]

There still seems to be some confusion over how the correct oil temperatue is maintained. Does the oil flow switch on & off to give the desired result? if so, this could effect ice melting, which has been said to take only a few seconds when engine power is demanded? (That was said on one report, but clearly did not happen when engine power was demanded on the incident in question)

I think there wasn't enough time for the ice to melt in this situation. They had been at low power settings for a while and it simply was too late to melt any/much before they hit the ground. I think that's why the new procedure calls for periodic power increases during letdowns.

[airfoilmod]

And from the info available, it would appear that how the Power is increased would play a part. If the FOHE has ice in the Fuel passages, care must be taken to avoid a sudden increase that disturbs the ice upstream, allowing it to drop and block completely the exit of the Fuel passage from the FOHE. The increase commanded by the A/T's produced large EPR's with accompanied Vibration; the FOHE is mounted on the Fan Shroud, after all, and full chat creates monumental vibration and acoustic energy. This might have shaken loose enough ice to pack up the exit, causing Rollback to ~1.15~. Again, the similarity of system performance would "defeat" the "expected" isolation of each engine from the other; at some point, systems are identical at the end of the pathway.

AF

[sooty655]

There still seems to be some confusion over how the correct oil temperatue is maintained. Does the oil flow switch on & off to give the desired result?


The differential pressure across the oil side of the exchanger will increase with cooler oil and decrease with warmer oil. So as the oil cools, the differential pressure valve will allow more oil to bypass the exchanger. However, this would be a progressive, rather than an on/off effect.

Sooty

[airfoilmod]

As Designed. If I'm not mistaken, the FOHE's intended purpose is to cool Oil not Heat Fuel. Warm Fuel is not a designed consequence, though obviously it gets taken into account. Down the road, if I may anticipate remediation, It will be considered insufficient to mitigate Icing Fuel Lines with Applied Power Profiling. There will need to be a mechanical solution. There is too much room for PE in a short term ("Advance the Throttles, this way, at this time," etc.). So a (Automatic) bypass will be installed, or Fuel Filters to sort small particle ice, or Fuel Heaters to melt ice, etc.

Perhaps one solution might include Fuel Bypass coordinated with Oil Bypass. If the Oil is sufficiently cool to bypass the FOHE, why continue to supply the Engine with FOHE derived Fuel? Link the bypasses to activate simultaneously??

AF

[sooty655]

Entirely agree with your last post.


If the FOHE has ice in the Fuel passages, care must be taken to avoid a sudden increase that disturbs the ice upstream, allowing it to drop and block completely the exit of the Fuel passage from the FOHE.


I thought the "possible problem" as identified by AAIB was an ice build-up on the inlet tubesheet of the FOHE. So the need would be to prevent ice release from upstream, not from within the FOHE. Once out of the tubes, the ice would immediately pass out of the FOHE.

If I read it right, the proposed RR interim fix addresses tube protrusion from the tubesheet, effectively making it smoother with less places for ice to catch and build up.

Sooty

[airfoilmod]

Perhaps demoting the FOHE to a secondary system, an ancillary instead of a singular, and Flight Critical component. If I was to propose a fix:

Build a new, shorter HE that has a "Y" at either end, allowing the provision of a gate valve that can Divert Fuel AROUND the Cannister to a Flow Only Bypass that supplies the HP directly in Cold Cruise. If the HE is Bench Built and conforms to existing Entry Exit Plumbing, It could be fitted in a scheduled C or D break, for uninterrupted revenue and Plumbing redesign. I'll call my patent Atty. Interested?

AF

[sooty655]

Stopping the ice build-up in the FOHE is IMHO addressing the symptoms, not the disease. If there is sufficient incipient ice in the fuel flow, when the holes in the cheese line up it will find somewhere to accumulate.

Wouldn't it be better to stop the ice at source, or at least stop it being released into the engine?

Sooty

[airfoilmod]

The Problem isn't Ice, it's water. "In Spec." Fuel has it and at very low temps it takes shape as granular microscopic particles. As such, it does no harm. At Cruise, in VERY low temp. over many hours, the ice melts and refreezes in the FOHE. It can reaccumulate at the small bore exits to the HP's., cause cavitation and starvation, as discussed. Heating, melting at the entry and immediately refreezing downstream is the problem. Oil cooling is not necessary at this point, indeed, the Oil (mostly) bypasses the FOHE anyway., so why direct the Fuel through a periodically unnecessary Path?

The solution isn't water free Fuel, which is impossible anyway; but directing Fuel around vulnerability in the Fuel Path when it may create problems.

AF

[keel beam]

SOOTY "Stopping the ice build-up in the FOHE is IMHO addressing the symptoms, not the disease. If there is sufficient incipient ice in the fuel flow, when the holes in the cheese line up it will find somewhere to accumulate"

KEEL BEAM
From 6th Sept 2008
"I am surprised this has not been more in the forefront of thoughts. I cannot say specifically for the B747SP, but certainly for the "classic" B747 and going back a few more years, the B707, they had dedicated fuel heaters. these were switched on by the flight engineer if he had a Fuel Filter Block warning light. After a set period of time, the fuel heater was switched off.

Looking at the diagrams on this thread, fuel heating is only supplied by the Fuel/Oil heat exchanger.

Just a thought ...."



How much money would need to be spent on having fuel that does not hold water and to have some sort of system on the fuel tanks to prevent water ingress through condensation etc.?

The Fuel Heater would be a simpler solution to the accumulation of ice.

Now the argument would be, where do you place the Fuel Heater, on the engine? At the front spar? In the tank? (I would go for the engine!)

[PAXboy]

(Non-pilot speaking)
But if you placed it in the engine - you have to pump the fuel there first ...?

My uneducated guess as to why fuel heaters were discontinued would be:
1) We have better fuel spec these days
2) We can save the weight and cost of these units
Followed by:-
3) It's worked well since we stopped installing fuel heaters ...

Humans usually have to learn things more than once.

[galaxy flyer]

Quick question and please excuse me for not going thru 115 pages to see it was already brought up:

Does the B777 have a fuel recirculating system to warm the stored fuel? My current bizjet does by recirc'ing fuel out of the oil cooler directly back into the wing tanks.

GF

[sooty655]

Paxboy
My uneducated guess as to why fuel heaters were discontinued would be:
1) We have better fuel spec these days
2) We can save the weight and cost of these units
Followed by:-
3) It's worked well since we stopped installing fuel heaters ...



And don't forget that the energy to heat the fuel is paid for in increased fuel burn. Only a small proportion of that comes back in the efficiency gain of hotter fuel for combustion

[Smilin_Ed]

And don't forget that the energy to heat the fuel is paid for in increased fuel burn. Only a small proportion of that comes back in the efficiency gain of hotter fuel for combustion

But the heat recovered by the necessary function of cooling the oil would otherwise be thrown away.

[precept]

************************************************************
NTSB PRESS RELEASE
************************************************************
National Transportation Safety Board
Washington, DC 20594
FOR IMMEDIATE RELEASE: March 11, 2009
SB-09-11
************************************************************
NTSB ISSUES URGENT SAFETY RECOMMENDATION TO ADDRESS ENGINE
THRUST ROLLBACK EVENTS ON B-777 AIRCRAFT
************************************************************
Washington, DC - Following two engine thrust rollback events
on Boeing 777 aircraft powered by Rolls-Royce engines, the
National Transportation Safety Board issued an urgent safety
recommendation today calling for the redesign of a Rolls-
Royce engine component. The Safety Board also recommended
that, after the redesign is completed, the new system be
installed on all affected B-777 airplanes at the next
maintenance check or within six months.
These recommendations are being issued in response to the
findings in two investigations - an accident and an incident
- involving engine thrust rollbacks on Boeing 777-200ER
airplanes powered by Rolls-Royce RB211 Trent 800 Series
engines. In both cases a build-up of ice (from water
normally present in all jet fuel) on the fuel/oil heat
exchanger (FOHE) restricted the flow of fuel to the engine,
resulting in an uncommanded engine rollback.
The first event, which is still being investigated by the
UK's Air Accidents Investigation Branch (AAIB), occurred on
January 17, 2008, when a Boeing 777 experienced a dual
engine rollback on final approach and crashed short of the
runway at London's Heathrow International Airport. One
passenger was seriously injured, eight passengers and four
of the flight crew sustained minor injuries; the airplane
was substantially damaged.

The second event occurred on November 26, 2008, when a Delta
Air Lines Boeing 777 experienced a single engine rollback
during cruise flight over Montana while en route from
Shanghai to Atlanta. Normal operations resumed after the
flight crew followed Boeing's published procedure to recover
engine performance; the airplane landed safely in Atlanta.
Testing in support of the UK accident investigation led
Boeing to develop procedures to help prevent ice
accumulation, and to recover thrust in cases of ice
blockage. As more information from the Delta rollback event
was developed, Boeing modified the procedures, which became
the basis of an airworthiness directive issued by the
Federal Aviation Administration.
While the procedures may reduce the risk of a rollback in
one or both engines due to FOHE ice blockage, they add
complexity to flight crew operations, and the level of risk
reduction is not well established. And because the recovery
procedure requires a descent, the aircraft may be exposed to
other risks such as rising terrain or hazardous weather, or
the inability to achieve maximum thrust during a critical
phase of flight, such as during a missed approach.
Because of these hazards, the Safety Board has determined
that the only acceptable solution to this safety
vulnerability is a redesigned FOHE that would eliminate the
potential of ice build-up. On February 23, 2009, Rolls-Royce
indicated that a redesign of the FOHE was underway, and that
they anticipated the redesign to be tested, certified and
ready for installation within 12 months.
"With two of these rollback events occurring within a year,
we believe that there is a high probability of something
similar happening again," said NTSB Acting Chairman Mark V.
Rosenker. "We are encouraged to see that Rolls-Royce is
already working on a redesign, and we are confident that
with the FAA and EASA (European Aviation Safety Agency)
overseeing the process, this flight safety issue - even one
as complex as this - will be successfully and expeditiously
resolved."
The NTSB has made the following two recommendations to both
the Federal Aviation Administration and the European
Aviation Safety Agency:
Require that Rolls-Royce redesign the RB211 Trent 800 series
engine fuel/oil heat exchanger (FOHE) such that ice
accumulation on the face of the FOHE will not restrict fuel
flow to the extent that the ability to achieve commanded
thrust is reduced.
Once the fuel/oil heat exchanger (FOHE) is redesigned and
approved by certification authorities, require that operators
of Boeing 777-200 airplanes powered by Rolls Royce RB211 Trent
800 series engines install the redesigned FOHE at the next
scheduled maintenance opportunity or within 6 months after the
revised FOHE design has been certificated, whichever comes
first.
The NTSB and AAIB will continue to work together closely on
both of the rollback events as each of the investigations
move forward.
Safety recommendation letter to the Federal Aviation
Administration:
http://ntsb.gov/Recs/letters/2009/A09_17_18.pdf (http://ntsb.gov/Recs/letters/2009/A09_17_18.pdf)
Safety recommendation letter to the European Aviation Safety
Agency: http://ntsb.gov/Recs/letters/2009/A09_19_20.pdf (http://ntsb.gov/Recs/letters/2009/A09_19_20.pdf)
Image: Ice accumulation on the inlet face of a Rolls-Royce
RB211 Trent 800 Series Fuel/Oil Heat Exchanger during
testing >>> http://www.ntsb.gov/Pressrel/2009/FOHEface.jpg (http://www.ntsb.gov/Pressrel/2009/FOHEface.jpg)
###
NTSB Media Contact: Peter Knudson
(202) 314-6100
[email protected]
************************************************************